Thank you CafeRacer. I'm not sure of the exact reference of my polerouter, but it's a cal 215 first gen (post patent pending but not a 215-1), also a no date. Guessing 1959-1960 vintage.
I actually had the original crown for my watch, it is domed and like the ones you've linked, but unfortunately the stem broke flush in the crown and it can't be salvaged. I don't have calipers but it seems to be around 4.5-5mm in diameter.
The crown can definitely be salvaged! Don't throw it away...
The stem is made of a different alloy of iron that can be selectively oxidised out of the crown.
There are many methods people swear by, but i've succeeded in removing a broken stem from a Polerouter crown by soaking it in concentrated bleach for about 6-8 hours, and periodically scratching out the rusted stem remnants with a pin (every hour or so...).
Oh wow, thanks for the tip. I will give it a try!
...And if your Polerouter case diameter is 33.5 mm diameter, it is probably a 20357-x, if it is 35.5 mm then probably a 20360-x.
Or even easier, in this case, you can discern between the two by the lug width (18 mm for 20357, and 19 mm for 20360).
I believe it's 33.5mm, I measure 34mm by measuring tape. Also I have a 18mm strap on it now and it fits well, so I'm guessing it's a 20357.
Crown is soaking in bleach now hoping this works
Concentrated bleach sounds very aggressive (and stinky). I use Alum. You can buy it in the spice section at your local grocery store. I fill a shot glass with water and add about 1/2 tsp of alum, stir and simply drop in the crown. (cover the glass with a lid to keep evaporation down). It takes days but safe. The steel stem slowly bubbles away to the point where it looks like it was never there. Many others on the list do the same. Never failed for me.
The correct crown for a Polerouter/Polarouter is specific to the model reference number.
https://universalgenevepolerouter.com/guide-to-locating-model-reference-and-serial-numbers/
All stems are the same thread for most (if not all) Polerouters (and UG perhaps) from this era.
Emily - what is the model reference of your Polerouter?
Timo - a 20360 should have the larger domed style, one that fits over the case tube of the 20360 and is 5.20-5.25mm diameter.
There are some crowns that look very similar on the outside, but are not interchangeable between references due to the internals and different sized case tubes for different references. They will fit the stem of course, but will not fit over the case tube... Ive run into problems a couple of times but have not yet gotten to the bottom of it (the differences are very small).
EDIT: Here are a couple of examples of what I believe to be the correct 20360 reference crown.
They wear down and become more rounded around the edges, but the two here look quite sharp/new:
https://shop.hodinkee.com/products/a-1950s-universal-geneve-polerouter-automatic?variant=31678302468
http://claremontvintage.com/shop/watches/ug_44/
Hope this helps...
