The four sizes that cover 95% of leisure boats
Production stainless rail in Europe ships in four standard outer diameters: 22, 25, 30 and 32 mm. Anything outside that range is either custom rigging on a superyacht or 1990s aftermarket. If your boat was built in the last 25 years, you almost certainly have one of those four.
The job is figuring out which one, and the difference between 25 and 30 mm is hard to eyeball from across a deck. Here are three ways to know for sure.
1. Caliper
The certain answer in 10 seconds. A €15 plastic vernier caliper from any hardware store does the job. Open the jaws around the rail at any clean spot, not on a weld or a junction, and read the number. If it falls between two standard sizes by less than half a millimetre, round up: the cradle inserts in our Base mounts have a 0.4 mm tolerance for grip, so the larger size will clamp the smaller rail comfortably while the reverse won't fit at all.
2. String
Wrap a piece of string, fishing line or even a strip of paper around the rail once. Mark where it overlaps. Lay it flat on a ruler. That length divided by 3.14 is your diameter.
- 69 mm circumference → 22 mm
- 78 mm circumference → 25 mm
- 94 mm circumference → 30 mm
- 100 mm circumference → 32 mm
This is the field method we use when an operator photo arrives and the caliper got left at home. Off by a millimetre is usually rounding error, use the table above to snap to the nearest standard.
3. The coin trick
A 5-cent Euro coin is 21.25 mm in diameter, almost exactly the same size as a 22 mm rail. Hold it next to the rail.
- Coin and rail look identical → 22 mm
- Rail clearly thicker → 25 mm
- Rail roughly the width of the coin plus a 2 mm gap → 30 mm
- Rail noticeably thicker than a 5-cent coin with room to spare → 32 mm
Two euro coins side-by-side (about 50 mm total) makes for a great visual reference when you're staring at a 30 vs 32 mm rail and can't decide.
A note on painted rails
Paint adds 0.3 to 0.5 mm of diameter depending on coats. If your rail is painted (rare on sailing yachts, common on motorboats), order one size up from your measurement.
Stuck? Send us a photo.
Mail a photo of your rail with a 5-cent coin held next to it to hello@adriafab.com and we'll tell you the size within an hour during EU office hours. Free of charge, no obligation.
