20 mm watch strap guide: sizes, materials and NATO straps
What a 20 mm watch strap is, how to check your watch takes one, the main strap types, how NATO straps got their name, and how to care for each.
20 mm watch strap guide: sizes, materials and NATO straps
A 20 mm watch strap is 20 mm wide where it meets the lugs. Here is what that means, which materials and types come in the size, and how NATO and Zulu straps differ, with each source named.
A 20 mm watch strap is 20 mm wide where it meets the watch, and it suits a watch with a 20 mm lug width. Lug width is the gap between a pair of lugs, so the strap has to match it. Past width, straps differ in length, thickness, buckle size, material and how they attach. We are a watch company, so we use the published numbers of the Vannin Field Watch, which is coming soon, where they help. This guide names no prices, links to no shops and names each source.
What size is a 20 mm watch strap?
A 20 mm watch strap is 20 mm wide at the lug end, and it is made for watches with a 20 mm lug width. That is the one number that decides whether a strap fits between the lugs. Length, thickness and buckle width are separate numbers, and the diagram shows where each is taken.
Our guide to watch lugs covers lug width, spring bars and the 19 mm and 21 mm question in full, so we do not repeat it here. Watch & Strap, a strap maker, calls 20 mm one of the most versatile sizes and says many traditional watches use it, field watches among them. It warns against assuming that every watch from one brand shares a size, because case diameter, production year and reference can all change the lug width.
How do I know if my watch takes a 20 mm strap?
Look up the lug width on the maker's page, or measure the gap between the inner edges of a pair of lugs. Crown & Buckle says the lug width of most watches can be found on the maker's or a retailer's website, and that you can also measure it with a calliper or a ruler. Hamilton is one maker that publishes it: its Khaki Field Mechanical 38 mm is listed with a 20 mm lug width and a textile NATO strap.
Timex says to measure the lugs rather than the old strap, because that gives a more accurate figure. It adds that many straps have the size printed or stamped on the underside, though the marking can wear away. Our lug guide gives the measuring steps, including why the inner edges are the ones to use.
The gap is necessary but may not be the whole story. Watch & Strap says a standard 20 mm strap normally fits with spring bars, but that for drilled lugs, quick-release bars or a proprietary integrated attachment the fitting method matters just as much as the width. If the maker does not say how a watch takes a strap, ask the maker.
What are the main types of 20 mm watch strap?
The main types are leather, NATO and Zulu nylon, rubber and silicone, canvas and sailcloth, and metal bracelets. Table 1 sets out what makers and strap specialists say about each. Every line is attributed, and the table summarises their words rather than ranking the types.
Leather comes in the widest range. Holbens describes suede and nubuck as softer and more casual, and says they work well with field watches and vintage-inspired designs. Thickness is a real variable: WatchGecko warns that where the lug holes sit very close to the case, a thickly padded leather strap may not fit or may scuff against the case.
Rubber is not one material. Holbens separates FKM, which it describes as resistant to heat, sunlight and salt water, from NBR and natural rubber, and says silicone is common in inexpensive straps. BluShark adds a fitting point: FKM rubber is less flexible than nylon, so it is a poor choice if you are trying to fit a strap slightly wider than the lugs.
Fabric straps vary just as much. Holbens lists nylon, Perlon, canvas, Cordura and elastic woven straps as different constructions, and says water resistance varies by construction. On a metal bracelet, Holbens advises confirming compatibility with the case rather than relying on lug width alone, since end links can be specific to a model.
| Type | What makers and strap specialists say | Water | Care |
|---|---|---|---|
| Leather | Holbens says leather offers the widest range of textures, finishes and thicknesses, and that thick or heavily padded leather may not suit every watch. Shinola says leather is the strap type most affected by moisture, sweat and sunlight. | Holbens: most leather is not intended for swimming or repeated soaking. | Shinola: avoid water and excess sweat, and store the watch flat in a dry spot away from sunlight. Hodinkee: avoid soaking, and condition the leather once it is dry. |
| NATO and Zulu (nylon) | Holbens says nylon is lightweight, durable and dries relatively quickly, and that thickness and weave vary widely. Crown & Buckle lists the nylon in its NATO range at 1.25 mm to 1.6 mm thick. | Shinola: water resistant, not waterproof. | Crown & Buckle: hand wash with mild soap and warm water, then air dry. Hodinkee: avoid hot water and the dryer. |
| Rubber and silicone | Holbens says rubber needs little maintenance and includes FKM, NBR and natural rubber, while silicone tends to attract lint and dust. Hodinkee notes that "rubber" is often a loose term that also covers silicone. | Holbens: the simplest choice for regular swimming, salt water and pool use. Shinola: silicone is water resistant. | Hodinkee: rinse under warm running water with mild soap and keep out of direct sunlight. Shinola's advice for its own silicone straps is not to use soap, so follow your strap maker's page. |
| Canvas and sailcloth | Holbens says canvas looks more substantial than most nylon and ranges from soft to structured, and that sailcloth-style straps use synthetic or embossed materials for better resistance to water and wear. Watch & Strap calls sailcloth more structured and water-ready than standard canvas. | Holbens: varies by model, so check the individual strap. | Watch & Strap: wipe clean with a lightly damp cloth. Holbens: care depends on the whole construction, including any lining. |
| Metal bracelet | Holbens says bracelets are durable and easy to clean but heavier than most straps, that some need tools for sizing, and that end-link compatibility can be specific to a watch model. | Holbens: unaffected by ordinary water exposure, provided the watch itself is suitably water resistant. | Shinola: expect scratches over time, wash with water, use a toothbrush in the gaps and dry them fully. |
What is a NATO strap?
A NATO strap is a one-piece strap, usually nylon, that threads under the watch through both spring bars, with the buckle and the loops, called keepers, on the strap itself. The name comes from a British Ministry of Defence strap, and today it is used for almost any pass-through strap in any colour.
Crown & Buckle says every NATO is a long one-piece strap that passes underneath the watch, and that most also have a second flap of strap under the watch, held by a floating keeper. The first purpose of that flap, it says, was to stop the watch sliding along the strap. The same maker puts its standard and premium NATO straps at 1.25 mm thick and its heavy-duty ones at 1.6 mm, and says the heavy-duty version is about as thick as a one-piece strap gets.
Because the strap runs under both spring bars, writers say the watch stays attached if one bar fails. SJX Watches says the watch would hang by the remaining bar. Sources differ on which part gives that protection. Crown & Buckle credits the pass under both bars, while StrapsCo credits the second layer. None of this makes a damaged spring bar safe to ignore.
NATO straps are common on field watches. Hamilton, for example, supplies its 38 mm Khaki Field Mechanical on a textile NATO strap. Our guide to what a field watch is covers the British military thread behind the style, including CWC.
Why is it called a NATO strap?
It is called a NATO strap because the British Ministry of Defence strap carried a NATO Stock Number, not because NATO designed it. NATO's own history page says the strap was created by the British Ministry of Defence in 1973 and that its stock number was eventually shortened into the name NATO strap. It adds that it is not a NATO-branded strap but an item used by the forces of a NATO member.
The primary document is the ministry's Defence Standard 66-47, Issue 2, dated 30 March 2001, in a copy hosted by a watch retailer. Its history record lists the standards it replaced, which is where the dates in Table 2 come from. It specifies a heat-welded nylon ribbon strap 20 mm wide, and lists two NATO Stock Numbers, one for Navy and Army use and one for the Air Force.
Sources differ on several details, so here is where they part. One strap retailer, Majestix, ties the 1973 date to Def Stan 66-47, but that document's own history record shows the 1973 standard was 66-15, with 66-47 following in 1992. The standard's text says the colour is grey, while NATO's page and SJX Watches call it Admiralty Grey. NATO's page, the 2001 standard and af0210strap's account of the 1973 drawing all give 20 mm, whereas Strap Swapper says the first strap was 18 mm. We use 20 mm, and we cannot settle which is right for the earliest straps.
The nickname G10 is also unsettled. NATO's page says it comes from British Special Forces having to fill in a G-1098 form to be issued the strap. SJX Watches says it is named after the form needed to order the strap. af0210strap, on the other hand, ties it to two Army forms, G1033 for an individual soldier and G1098 for a unit's stores. G10 is also the name of a watch: CWC says its 1980 G10 was the first quartz watch issued to British forces. We found no source linking the two names, so we keep them apart.
| Date | What the source says | Source |
|---|---|---|
| 1954 | The RAF issued a heat-welded nylon strap, listed as 6B/2617, 16 mm wide. | af0210strap, a maker of reproduction straps |
| 1964 | In Goldfinger, James Bond's Rolex Submariner is on a striped regimental strap. NATO says this is not a NATO strap, because that strap was created nine years later. af0210strap describes it as a 16 mm nylon RAF strap. | NATO; af0210strap |
| 30 November 1973 | Def Stan 66-15 Part 1, Issue 1, "Strap (Nylon)", carries this date in the record inside Def Stan 66-47. SJX Watches also dates the two-piece nylon strap to Def Stan 66-15 of this day. | Def Stan 66-47 Issue 2; SJX Watches |
| 31 January 1974 | Def Stan 66-15 Part 2, Issue 1, "Strap (Leather/Nylon)", carries this date. | Def Stan 66-47 Issue 2 |
| Late 1970s | af0210strap says the name NATO for a watch strap dates from the late 1970s, as a casual reference to the strap's NATO Stock Number. We found no source that dates the name more exactly. | af0210strap |
| 13 November 1992 | Def Stan 66-47, Issue 1, carries this date. | Def Stan 66-47 Issue 2 |
| 30 March 2001 | Def Stan 66-47, Issue 2, "Strap, Wrist Watch", replaces the earlier standards. It specifies 20 mm nylon ribbon in grey, BS 4800 reference 18B25, with welded joints and sealed ends. | Def Stan 66-47 Issue 2 |
Are NATO straps and Zulu straps the same?
No, though the names are often mixed up. Both are one-piece nylon straps that pass under the watch, but a Zulu usually has thicker nylon and heavier, rounder hardware. Sources describe the difference through hardware, thickness and the number of layers under the case, and they do not always agree, so Table 3 sets out what each says.
In practice, check the product photo and the listed thickness rather than the name. Because "Zulu" is a trademark, Strap Swapper notes that many sellers use other names, such as 5-ring or heavy-duty NATO.
| Feature | NATO | Zulu |
|---|---|---|
| Hardware | StrapsCo: thinner, more rectangular keepers and a tang buckle. | StrapsCo: rounder, thicker hardware. Majestix, a strap retailer, says the keepers are made from round rod. |
| Nylon thickness | Strap Swapper: 1.2 mm. Majestix: about 1 mm. Crown & Buckle: 1.25 mm for its standard NATO. | Strap Swapper: 1.5 mm or more. Majestix: 2 mm to 3 mm. The sources do not agree. |
| Layers under the case | Majestix: two, with a retaining flap. StrapsCo: commonly an extra piece of strap on the underside. Crown & Buckle: most have the flap. | Majestix: one on a 3-ring Zulu and two on a 5-ring. StrapsCo: 5-ring Zulus include the extra piece and 3-ring Zulus do not. |
| Origin and name | A British Ministry of Defence strap, with a Defence Standard (Table 2). | Strap Swapper says it has no documented military origin. Majestix says the style predates 1973 and that the name most likely comes from Zulu time, while Strap Swapper calls that unconfirmed. |
| Name as a trademark | Not applicable. | A US trademark record lists Maratac as owner of ZULU for watch bands and straps, with a first use of 28 February 2005 and registration on 6 April 2010. Strap Swapper gives a different serial number and registration date. |
How do you wear a NATO or Zulu strap?
A NATO or Zulu strap threads through the watch instead of clipping on, and the spring bars stay in the lugs. In Crown & Buckle's instructions for a nylon NATO, the long section passes between the 12 o'clock spring bar and the case, then between the 6 o'clock spring bar and the case, so the strap runs under the watch. The long section then goes back through the floating keeper and the case is centred between the keepers. T3 describes the same outline.
Crown & Buckle's separate wearing guide covers the buckle end. The long end goes through the buckle, the tail passes up through both keepers, and any excess folds back into a keeper. It calls the strap "one size fits most", and says very large wrists may have no excess to tuck.
That describes a nylon strap. Crown & Buckle says a leather NATO can be scratched by the case if it is pulled through the spring bars, so it fits leather ones another way. It says the same method suits nylon straps on watches with little room between the spring bar and the case. We give no removal or refitting steps here. If you are unsure, ask a watchmaker.
Strap thickness and the gap between the lugs
Thickness matters because a pass-through strap puts nylon between the spring bar and the case, and a standard NATO puts two layers under the watch. Case designs differ in how much room they leave, and no source gives a gap figure that applies to every watch.
Several sources describe the symptoms. Watch & Strap says resistance when fitting a strap usually means the width is wrong, the spring bar is misaligned or the strap is too thick for the case design. BluShark says a watch with a tight gap between case and spring bars is harder to fit with a thick strap. Crown & Buckle calls its 5-ring heavy-duty NATO its bulkiest nylon strap, and Majestix says a NATO sits higher off the wrist than a 3-ring Zulu because of the second layer.
If a maker publishes lug width but not clearance, ask the maker.
Strap length and fit
Length is a separate measurement from width, and makers quote it two ways. Carl Friedrik says a two-piece strap is written as two numbers in millimetres, the longer tail side first, for example 125/75, with the buckle left out. A NATO is one piece, so it has one length. Crown & Buckle quotes 280 mm for its standard, premium, defence and HD NATO straps and 290 mm for its Supreme range, and gives wrist sizes of roughly 5.75 to 9.0 inches and 6.0 to 9.25 inches.
Those wrist ranges assume an average watch, which Crown & Buckle takes as a 40 mm case with a 47 mm lug-to-lug. It adds that case size, lug shape, strap thickness and personal taste for snugness all change the result. Timex lists men's lengths as short, regular, long and extra-long, from 6.25 inches up to 9.25 inches. SecTime gives a formula: subtract the watch's lug-to-lug from your wrist circumference to get the fitted strap length, and aim to fasten on a middle hole.
The sources start from different places, so treat each as a guide, not a rule. For the wrist side, our watch size guide explains how to measure your wrist circumference and the flat across the top.
Strap width, buckle width and strap notation
A strap has two widths: the lug end, which must match the lug width, and the buckle end, which must match the buckle. Holbens writes them as two numbers, lug width first, so a 20/16 mm strap is 20 mm at the lugs and 16 mm at the buckle. That change in width is called taper. Zulu Diver defines it the same way and says not all straps have one.
Holbens says no taper is common on some sport, dive and military-style straps. It also says a replacement buckle has to match the buckle-end width, not the lug width, and that the strap width, not the taper, decides whether it fits between the lugs. If a listing gives only one width, check whether it means the lug end or the buckle end.
Quick-release bars and spring bar safety
Spring bars hold the strap on, so handle them with care. WatchGecko describes a spring bar as a round steel bar with spring-loaded telescopic ends that compress to fit and spring back to fill the lug holes. It says quick-release bars let you change a strap without tools and keep the bar attached to the strap, so there is no chance of losing it or sending it across the room.
T3 warns that bars under pressure can fly, so keep a tight grip and keep the watch away from your eyes. Barton advises working on a soft cloth, says a razor blade, credit card or small knife risks scratching the case or the band, and recommends a professional if you are unsure. Watch & Strap says never to force a strap between the lugs, and to give it a gentle pull after fitting to check both ends are seated.
We would add only this: if a strap will not go on without force, stop and ask a watchmaker.
Can you use a 19, 21 or 22 mm strap on 20 mm lugs?
Sources differ, and our lug guide covers the 19 mm and 21 mm cases in detail. BluShark, writing about odd lug sizes, says sizing down by 1 mm leaves a gap of about 0.5 mm each side that most people barely notice. Watch & Strap says a strap 1 mm out can look untidy or need force.
For wider straps, BluShark says the strap has to be compressed at the spring bars. That can work with thin, flexible nylon, but is hard or impossible with rigid FKM rubber or tight spacing. Its example is a strap 1 mm wider than the lugs. A 22 mm strap is 2 mm wider than 20 mm lugs, so we expect it to be harder, which is our reading, not a source's. We do not call any of it fine or wrong, and we say never force a strap.
How to care for a 20 mm strap by material
Take the strap off before cleaning, and dry it fully before it goes back on the watch. Hodinkee advises removing a rubber strap before washing it, unless you completely trust the watch's water resistance. Beyond that, care depends on the material, and Table 1 gives each maker's words.
A few differences are worth knowing. Crown & Buckle says to rinse a nylon strap with fresh water after swimming, to wash away chlorine or salt. Hodinkee warns that heat can damage nylon and says it has seen NATOs melt in a dishwasher. For leather, Shinola and Hodinkee both advise against soaking it. On silicone the sources disagree: Hodinkee uses mild soap, while Shinola says not to use any soap on its own silicone straps. Follow the maker's page for the strap you own.
How to choose a 20 mm strap
Choose by how you use the watch, how wet it will get and what you wear it with. Holbens suggests leather as the usual starting point for dress and traditional everyday watches, rubber for swimming, sport and frequent water, textiles such as nylon for hot weather and light weight, and steel where durability matters most. It says there is no single best material.
For field watches, Holbens says suede, nubuck, distressed leather, canvas, nylon, Perlon and understated rubber can all work. Watch & Strap adds that a second strap gives a watch more range, with leather for the office and rubber or sailcloth for rain and travel. Both are strap sellers, so treat the advice as theirs.
A strap does not change what the watch itself is rated for. Our guide to water resistance ratings explains what the numbers on a dial mean, and Holbens adds that steel suits water only if the watch is suitably water resistant.
The Vannin Field Watch and 20 mm straps
The Vannin Field Watch has a published lug width of 20.0 mm and a published strap width of 20.0 mm. It is coming soon, and this guide does not say which straps will go on it.
You can see the watch on the Vannin Field Watch collection page. For the case measurements behind the lug width, see our watch lugs guide.
Our straps page introduces the future Vannin straps and accessories collection.
Frequently asked questions
What size is a 20mm watch strap? A 20mm watch strap is 20mm wide at the lug end, where it meets the watch, and it is made for watches with a 20mm lug width. Length, thickness and buckle-end width are separate figures. Strap makers such as Watch & Strap call 20mm a versatile size, and many traditional watches, field watches among them, use it.
How do I know if my watch takes a 20mm strap? Check the lug width on the maker's page, or measure across the gap between the inner edges of a pair of lugs with a ruler or callipers. Timex says to measure the lugs, not the old strap, and that many straps have the size printed on the underside. If the maker does not publish it, ask.
What is a NATO strap? A NATO strap is a one-piece strap, usually nylon, that threads under the watch through both spring bars, with a buckle and keepers on the strap. It comes from a British Ministry of Defence 20mm nylon strap, specified in 1973. Crown & Buckle adds that most also have a second flap of strap under the watch.
Why is it called a NATO strap? NATO's own history page says the British Ministry of Defence created the strap in 1973, and that its NATO Stock Number was eventually shortened into the name. NATO did not design or brand it. Sources differ on the nickname G10, which NATO's page links to a G-1098 requisition form.
How do you wear a NATO strap? On a nylon NATO, the long section passes between each spring bar and the case, so the strap runs under the watch. The long end then goes through the buckle, the tail through the keepers, and any excess folds back into a keeper. This is Crown & Buckle's outline. If unsure, ask a watchmaker.
Are NATO straps and Zulu straps the same? No, but sources disagree on the difference. A Zulu usually has thicker nylon and rounder, heavier hardware, and a 3-ring Zulu has one layer under the case where a NATO has two. Strap Swapper says Zulu has no documented military origin. Thickness figures vary by source, so check the listing.
Can I put a 22mm strap on a 20mm watch? Sources differ. BluShark says a wider strap must be compressed at the spring bars, which can work with thin nylon but rarely with rigid rubber, using a 1mm example. A 22mm strap is 2mm wider, which we expect to be harder. We do not call it fine or wrong. Never force a strap.
How do you measure a watch strap? Measure width at the lug end in millimetres, and length without the buckle. Carl Friedrik says to measure the tail side and buckle side separately on a two-piece strap, and Holbens says the buckle-end width decides which buckle fits. A NATO has one length. If a strap already fits well, look for a similar one.
Sources and specifications last checked 24 October 2026. Tell us if something has changed.
Related reading
Vannin Watches Limited, registered in the Isle of Man (company no. 139401C). Registered office: Thie-Ny-Dhreem, Ballaragh, Laxey, IM4 7PW.