Hello, I just acquired a grade 105, model 5, serial no 3306464, that seems to need a balance staff. According to the listing of staffs here, there are two sizes for the size 16 models. Part no. 2720 and 3720. The staff in my watch looks good, as do the balance jewels, but seems too short, so I am wondering which staff is the correct one. # 2720 is slightly longer. Also the listing mentions M1890 for 2720 and M1902 for 3720. Can anyone explain this to me? Thanks.

The books I have are not very clear but it looks like a 3720 5.15mm for 16 size exposed winding wheels model 5 the 2720 is 5.60mm.

Now do not assume that the staff in there is even a Hampden if it has been changed it may well be whatever seemed to fit, you could measure the length and see if its close to either above. any glue holding roller on or badly beaten to fit a undersize staff ?, also look see if it has been filed down, are there gouges under the cock, bent cock, jewels changed incorrectly not seated etc , the first rule with pocket watches is assume nothing all kind of quick fixes go on, check the serial number on the balance if it has one often if people cant change a staff the put a new balance complete is to get it sold I had one yesterday like that, I just had a very rare Ball that was destroyed by people filing bridges away to make room for a severe balance wobble after a bad staff change, (ebay special) the watch is now scrap