Guide
Spring Bar Sizes Explained
Spring bars are the small sprung pins that hold a strap between the lugs. Buying replacements is easy once you know the two numbers that matter, length and diameter, and a couple of design details.
How a spring bar works
A spring bar is a thin steel tube with a spring inside and a tip at each end. Compress the tips and the bar gets shorter; let go and they push out into small holes on the inside of each lug. The strap's end wraps around the bar, or the bar passes through a channel in it.
Length: matches your lug width
Spring bars are sold by the lug width they fit: a 20mm bar for 20mm lugs, a 22mm bar for 22mm lugs, and so on. If your watch takes a 20mm strap, it takes 20mm spring bars. Odd widths such as 19mm and 21mm have matching bars too.
Diameter: what the numbers mean
Diameter is the thickness of the tube. It has to suit the hole or channel in your strap. A fat bar won't go through a thin leather strap's channel, and a thin bar rattles inside a rubber strap made for a fat one.
| Diameter | Where you'll see it | Watches in our index | Examples |
|---|---|---|---|
| 1.5mm | Thin bars for small, light watches — common on digital Casios and some vintage pieces. | 2 | Casio F-91W, Casio A168 Vintage |
| 1.8mm | The everyday standard (often sold as 1.78mm) on most dress, field and mid-size watches. | 20 | Seiko Alpinist, Seiko SARB033, Seiko Presage Cocktail Time |
| 2.0mm | A slightly sturdier bar used on many modern sports and dive watches. | 27 | Seiko Prospex 62MAS, Seiko Prospex Willard, Grand Seiko Snowflake |
| 2.5mm | ‘Fat’ bars, typical of Seiko and Tudor divers. Strong, but they need straps with larger holes. | 11 | Seiko SKX007 / SKX009, Seiko 5 Sports (5KX), Seiko Prospex Turtle |
The values above come from the watch pages in our index; each page lists the approximate bar diameter for that model. If you're unsure, measure the old bar with calipers. Even a 0.2mm difference can matter in a tight strap.
Fat bars
Many dive watches, Seiko's in particular, use 2.5mm “fat” bars. They're stronger and suit heavy rubber straps and thick NATOs. The catch is that many thin leather straps can't take them. If your watch has fat bars, either choose straps made for them or switch to thinner bars of the same length. That's fine for light straps, as long as the tips still sit securely in the lug holes.
Shoulders and tips
The shoulder is the small flange near each tip that a spring bar tool grips. Double-shoulder bars have two flanges at each end and are easier to remove where space is tight, such as with fitted end-links or thick straps. Single-shoulder bars are slimmer. Tip diameter matters on some watches too: small or vintage cases can have small lug holes that need thinner tips.
Quick-release bars
Quick-release bars have a small lever so you can swap straps without tools. They're ideal if you change straps often. They need a strap with a gap for the lever, so they suit most aftermarket leather and rubber straps but not every NATO or fitted bracelet.
Buying replacements
- Match the length to your lug width and the diameter to your strap.
- Choose stainless steel (often 316L) and buy a small multi-pack. They're cheap and easy to lose.
- Replace any bar that's bent, rusty or has a weak spring. A failing bar is the most common way watches get dropped.
Next step: how to change a watch strap.