What exactly is this?

[Ammar]

Hello everybody, 

I came across this tool, the listing says that this is a caliper but I'm not sure about that. 

Can you tell me what's this please, and is it usefull for some one like me who is just servicing watches for fun. 

[mbwatch]

It looks like it is a very old and incomplete truing caliper, used to find out if a wheel is bent out of round. The little nubs in the jaws would be used to hold wheel pivots. And that protruding post on the lower arm opposite the screw I would guess originally held another metal blade used for comparison against the wheel's rim.  The size of it and being sprung closed makes me wonder if it was meant for clocks rather than watches.

If that was its purpose, it is probably no longer useful since it is missing a part and is in terrible condition. Tools that do this can be bought for very little. 

It is also possible this is for something else entirely, and not a wheel truing caliper.

Here's a common style, picture randomly lifted from ebay. That black metal part on the post is what I think is missing from yours.

Edited February 21 by mbwatch

[Neverenoughwatches]

30 minutes ago, Ammar said:

Hello everybody, 

I came across this tool, the listing says that this is a caliper but I'm not sure about that. 

Can you tell me what's this please, and is it usefull for some one like me who is just servicing watches for fun. 

Funny I was just restoring a nice jewelled nibbed one of these 2 days ago. It is a truing poising tool , depending what the nibs are. I have a couple of traditional non jewelled ones as well. Ok for poising but there are better more accurate tools. The TruPoise bench tool works on the same principle of supporting the pivot ends.  Clean it up, restore the nibs and try it out on an old balance .

Looks rusty and the register arm is missing, if you haven't bought it I'd give it a miss.

18 minutes ago, mbwatch said:

It looks like it is a very old and incomplete truing caliper, used to find out if a wheel is bent out of round. The little nubs in the jaws would be used to hold wheel pivots. And that protruding post on the lower arm opposite the screw I would guess originally held another metal blade used for comparison against the wheel's rim.  The size of it and being sprung closed makes me wonder if it was meant for clocks rather than watches.

If that was its purpose, it is probably no longer useful since it is missing a part and is in terrible condition. Tools that do this can be bought for very little. 

It is also possible this is for something else entirely, and not a wheel truing caliper.

Here's a common style, picture randomly lifted from ebay. That black metal part on the post is what I think is missing from yours.

These calipers are much better for truing, poising one end and the other end for truing that have cone shaped nibs to support the balance pivots while truing.

[RichardHarris123]

Vintage tools are cool but sometimes they need to be just for display. If you want something functional don't buy them, if you want something cool on your bench, go for it.