A replacement strap fails for one of two reasons: the wrong lug width, or the right width with the wrong spring bar. Both are measurable before you buy, and both are cheap to get right — a strap that is 1 mm too narrow will pull out of the lugs under load, and one that is 1 mm too wide will not seat at all.
Measure the lug width first
The lug width is the distance between the inside faces of the two lugs on one side of the case, measured in millimetres. Measure it with a ruler or calipers with the old strap off; measuring with the strap on gives you the strap width, which is close but not always the same after wear. Common widths are 18, 20, 22 and 24 mm, with 19 and 21 mm on some Swiss cases.
If you cannot remove the strap, look up the case reference — the lug width is part of the specification. Do not guess between 20 and 22 mm: the difference is visible and the strap will not fit correctly.
Spring bars: the part that actually fails
Spring bars come in three relevant varieties. Standard bars have a fixed shoulder and rely on the lug holes; quick-release bars add a small lever so the strap can be changed without a tool; and fat bars (usually 1.8 mm or 2.5 mm) are needed when the lug holes are large. A 1.5 mm bar in a 2.5 mm hole rattles and can pop out under a sharp pull.
Check the bar diameter as well as the length. A bar that is too long will not compress into the lugs; one that is too short leaves the shoulder outside the hole and the strap can detach.
Strap length and fit
Wrist size determines length, not width. Measure your wrist with a tape, then add roughly 15 mm for the buckle and tang. A leather strap that is too long creases at the wrong point and cracks early; a metal bracelet needs the correct number of links removed from both sides rather than all from one, or the clasp sits off-centre.
Quick reference
| Case type | Typical lug width | Typical spring bar |
|---|---|---|
| Dress watch, 36–38 mm | 18–20 mm | 1.5 mm standard |
| Field watch, 38–40 mm | 20 mm | 1.8 mm standard or quick-release |
| Dive watch, 40–42 mm | 20–22 mm | 2.5 mm fat bar |
| Oversized chronograph, 44 mm+ | 22–24 mm | 2.5 mm fat bar |
Frequently Asked Questions
Can I use a 20 mm strap on 22 mm lugs?
No. It will fit between the lugs but leave a visible gap, and the spring bar shoulders will not seat properly. The strap can pull free under load.
Are quick-release spring bars as strong as standard ones?
For normal wear, yes. For diving or heavy use, a standard fat bar is the safer choice because the release lever is an extra failure point.
How do I remove a bracelet without scratching the lugs?
Use a spring bar tool with a forked tip, tape the lug edges, and push the bar straight rather than levering. Scratches come from the tool slipping sideways, not from the bar itself.
Do all brands use the same spring bar length for a given lug width?
No. Lug hole depth varies, so the correct bar length is lug width minus the depth of both holes. A bar sold as “20 mm” is intended for 20 mm lugs but may still be too long or short for a specific case.
The We Know Watches editorial team brings together over 40 years of combined watch collecting, trading, and repair experience. Our editors have owned and handled watches from every major brand — from entry-level Seiko 5s to Rolex, Omega, Patek Philippe, and independent Swiss watchmakers. We’ve bought and sold at auction, worked with authorized dealers, visited manufacturing facilities in Switzerland and Japan, and serviced hundreds of movements ranging from the Seiko 7S26 to the Longines L888. Every guide and review we publish is based on hands-on experience, original research, and consultation with professional watchmakers. We do not accept payment for reviews, and we clearly disclose when we use affiliate links.