Speedmaster replacement crown conundrum…

M'Bob · Tues. 5:21pm

One crown is listed as 069ST43018. It’s supposed to be for ref. 105.003, and all earlier references.

Another is 069ST43069. That one is supposed to be for 105.012 and later, as it is slightly smaller in diameter (6.5mm vs 6.8mm), with all other parameters being equivalent (tap, depth, tube).

The rationale is that the larger crown will not fit inside the later case crown guards. Yet…some sources on the net say they completely interchange, and others say the slightly larger crown, for the earlier models, will NOT fit the later 105.012, 145.012, 145.022.

Can anyone offer any clarity here? I’ve got a headache. Thanks.

WatchBreaker · Tues. 6:48pm

Mechanically, the two crowns fully interchange. Same tap, same post depth, same tube fit, so either one screws onto any of these stems and seals on any of these cases. Anyone who’s swapped them and had the watch work fine is reporting that truthfully.

The dispute is purely about clearance at the crown guards, and the margin is tiny. Going from 6.5mm to 6.8mm is only 0.15mm extra radius on each side, and that’s roughly the whole designed gap between crown and guard flank on the asymmetric case. So the 6.8mm crown in a 105.012/145.012/145.022 is a borderline fit that goes either way depending on the individual case: a case that’s been polished once or twice has slimmer guards and the big crown clears; a sharp, unpolished case may scrape or bind. Guard geometry also drifted slightly across the 145.022 generations, which adds more scatter. That’s why the internet can’t agree - people are honestly reporting opposite outcomes from the same swap on different cases.

So the practical rule stands: 069ST43069 (6.5mm) for the crown-guard references, 069ST43018 (6.8mm) for 105.003 and earlier. The small crown on a straight-lug case always works and just looks slightly undersized; the big crown on a guarded case is a gamble you don’t need to take. One caveat - the physical reasoning is solid, but I haven’t re-verified the part numbers and diameters against a catalogue, so treat those figures as the thread states them.

M'Bob · Tues. 7:50pm

Fabulous, clear, detailed answer. Much appreciated.

Caliber561 · Wed. 1:34am

WatchBreaker
Mechanically, the two crowns fully interchange. Same tap, same post depth, same tube fit, so either one screws onto any of these stems and seals on any of these cases. Anyone who’s swapped them and had the watch work fine is reporting that truthfully.

The dispute is purely about clearance at the crown guards, and the margin is tiny. Going from 6.5mm to 6.8mm is only 0.15mm extra radius on each side, and that’s roughly the whole designed gap between crown and guard flank on the asymmetric case. So the 6.8mm crown in a 105.012/145.012/145.022 is a borderline fit that goes either way depending on the individual case: a case that’s been polished once or twice has slimmer guards and the big crown clears; a sharp, unpolished case may scrape or bind. Guard geometry also drifted slightly across the 145.022 generations, which adds more scatter. That’s why the internet can’t agree - people are honestly reporting opposite outcomes from the same swap on different cases.

So the practical rule stands: 069ST43069 (6.5mm) for the crown-guard references, 069ST43018 (6.8mm) for 105.003 and earlier. The small crown on a straight-lug case always works and just looks slightly undersized; the big crown on a guarded case is a gamble you don’t need to take. One caveat - the physical reasoning is solid, but I haven’t re-verified the part numbers and diameters against a catalogue, so treat those figures as the thread states them.

Is there a source for this that isn't Claude?

WatchBreaker · Wed. 5:13am

Caliber561
Is there a source for this that isn't Claude?

Yes, it's a database on watchbreaker.com. You can also learn part names at the bench

Speedmaster replacement crown conundrum…

M'Bob

WatchBreaker

M'Bob

Caliber561

WatchBreaker

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