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Choosing the correct replacement crown?


Robbie010

Question

My latest project watch is a BFG 866, which states that it is (was) waterproof to 5atm. 

I have a stem but am missing the crown, there is no threaded tube on the case, so its not a screw down crown, but I’m struggling to find the right replacement.

The stem is 1mm diameter, the opening in the case is 2.5mm and I believe the crown should be 5mm. 

I assume the crown should have a tube with a rubber seal of some kind.....?

Am I best buying one of those cheapo eBay jobbies with assorted crowns?

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29 minutes ago, Robbie010 said:

The stem is 1mm diameter, the opening in the case is 2.5mm and I believe the crown should be 5mm. 

Your watch has no pendant tube, so I don't see how it can be water resistant, unless you fit one. Beside that a pendant tube is needed to avoid the crown wobble and the stem bend easily. The tube is measured on the ouside diameter, to match the seal on the crown.

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I assume the crown should have a tube with a rubber seal of some kind.....?

Yes, so called waterproof, Swiss style. 

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Am I best buying one of those cheapo eBay jobbies with assorted crowns?

All assortments are very useful especially you intend to do a lot of resturations on watches that match the boxes you have. And having the right part ready to fit is a great achievement.  Look the table which lists the sizes, see if there's what you need before buying.

Otherwise Cousins has a good selection of individual crowns also.

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Press-fit a pendant tube in that hole, there's a special tool for this. That's going to leave you with a pendant tube OD of 2.5mm. The crown fits over this to form a waterproof with a rubber seal inside the body of the crown. You have chosen 5.0mm crown diameter, you still need to know the tap size (metric diameter of the threads on the winding stem, commonly 0.9 but also other sizes). Those 3 numbers, plus the finish (stainless, gold, etc) and the type (waterproof, swiss style, domed, etc ) will find you a crown.

Older, cheaper, non-waterproof watches just have a hole with no pendant tube and no seal, or sometimes a notch in the case rather than a hole, so the movement with stem fits into the case and a press-on caseback holds the movement and stem in place (often seen in "ladies" cocktail bracelet watches)

 

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