The Promaster is one of the most capable watches anyone sells at its money. ISO-rated diving credentials, a movement you never wind or service for a battery, 200 metres, a proper unidirectional bezel. It is also, deliberately, one of the most neutral-looking watches at its money — which is precisely why the strap does so much of the work on it.
Change the strap and you change what the watch is. Very few watches at this price respond that dramatically, because very few are this capable and this plain at the same time.
The problem is finding out what size to order.
It Takes 20mm — and the Internet Is Not Reliable Here
The Promaster Diver and Marine families take 20mm. That covers the BN0150 series, the BN0151 and BN0156 variants, the BN0191 and BN0193 series, and the NY0040 Marine and Fugu references.
The best evidence is Citizen's own hardware: the factory replacement strap sold for the NY0040 and BN0150 is specified at a 20mm lug width. Independent specialists publishing per-reference data give the same figure, and so do owners who have measured theirs.
⚠️ And yet two large strap retailers publish something else — while contradicting themselves in the process. One has a dedicated "best straps for the Promaster Diver" page stating 18mm, while its own per-reference page for the same watch says 20mm. Another publishes a Citizen lug-width chart claiming the Promaster Diver "usually takes 22mm", while its own model page for a BN0150 reference says 20mm.
That is not a small thing. Those pages rank, people read them, and a strap ordered from either would not fit. If you have seen 18mm or 22mm quoted for a Promaster Diver, disregard it. Order 20mm.
One genuine exception: the larger Promaster cases — the big Aqualand-style and BJ8050-type references — do use other widths, including 22mm. If yours is one of the oversized ones rather than the standard Diver or Marine, measure the gap between your lugs before ordering, or send us the reference and we will confirm it.
The Spring-Bar Detail Nobody Mentions
This one is worth knowing before you buy, because it is the commonest complaint after a Promaster strap change and it is not the strap's fault.
Citizen's spring bars use unusually slim tips. An owner who measured a set with calipers found the ends at roughly 1.16–1.18mm — narrower than the tips on many aftermarket quick-release bars, and narrower than the lug holes are cut for on some third-party hardware. The result is a faint rattle or click when the watch moves.
The fix is simple: keep your original Citizen spring bars and use them with the new strap. Take them out of the factory strap, put them through the new one, and the fit is tight and silent. If your new strap arrives with quick-release bars and you notice any play, swap back to the originals — you lose the tool-free convenience and gain a strap that does not click.
Our guide to quick release explains the difference between the two kinds of bar and when each is worth having.
Two Case Shapes, Two Strap Shapes
Worth checking before you choose, because the Promaster line is not one case.
The round Diver cases — the 44mm BN0150 family and its relatives — have flat-faced lugs, and a straight-cut strap end is the right shape for them.
The cushion-cased references — the Fugu and its siblings — curve down into the lug the way a cushion case does, and a curved end continues that line where a straight cut leaves a small wedge at each corner.
Same width, different shape. It is the difference between a strap that fits and a strap that looks like it was made for the watch.
The Best Straps for a Citizen Promaster
On a diver, the bezel makes the colour decision, not the dial. Promaster dials are almost always black; the bezel is where the watch declares itself — black, blue, or the orange-accented references that the line is known for.
1. Black FKM Rubber — the upgrade the watch is waiting for
The factory rubber on a Promaster is functional and generic — moulded black with no particular character, the sort of strap that comes with a watch rather than one chosen for it. Replacing it with a properly made FKM rubber strap is the cheapest transformation available to this watch. Our straight-end FKM range is cut in 20, 22 and 24mm and is the right shape for the round Diver cases.
2. Orange — the colour this watch has actually earned
High-visibility orange is diving equipment rather than decoration, and on the orange-accented Promaster references it repeats something already on the watch instead of introducing something new. It is the one loud colour that reads as correct on a diver and as costume almost anywhere else.
3. A Curved End — for the cushion cases
If yours is a Fugu or another cushion-cased reference, the curved-end FKM range covers 20mm and follows the case line properly.
4. A Fine Coloured Line — for the blue-bezel references
The black LuxLine® strap with a fine blue line picks up a blue bezel without becoming the loudest thing on the wrist — the disciplined version of adding colour.
Leather is the one to think twice about. This is a 200-metre dive watch and leather is a decision not to use that. If you want a dress option, own it as a second strap rather than a replacement.
If Yours Came on the Bracelet
The steel Promaster bracelet is heavy and it holds heat in summer — two things you notice on a 44mm case. Moving to rubber takes real weight off and makes the watch considerably easier to wear in the conditions it was designed for.
And the bracelet goes back on whenever you want. Nothing is drilled, glued or modified. Our guide on taking a watch off its bracelet covers the rest.
The Bottom Line
20mm for the Diver and Marine families — not 18mm, not 22mm, whichever chart you were about to trust. Keep your original Citizen spring bars if a new strap rattles. Straight end for the round cases, curved for the cushion ones.
Every rubber strap we make carries a lifetime warranty and leather carries one year; shipping is free worldwide with no import costs, and more than 50,000 customers already trust us with their watches. Send us your reference if you own one of the larger Promasters and want the width confirmed.
