What is this?

[MrJeep]

I found this in a lot of tools that I recently purchased. It's 10"long, is spring loaded when you pull back on the knurled end and the 3 balls retract as the taper is withdrawn into the body. Has 4 hash marks on the blued area and a scale up near the knurled end. The only markings on the tool is OM or ON in script and made in Germany.

 

[Jeff Ivers]

Looks like a really fancy nail set.

 

[NUTTSGT]

Coarse, medium, fine ? threads per inch ?

 

[RoninB4]

I have some hole diameter gauges like this. Not meant for a precision measurement but a quick way to get within +/- .12 mm. The spring holds the taper in and you read the numbers. There are also graduated flat gauges for the same purpose. I may be wrong but that's what it looks like to me.

 

[larry_g]

Three point hole gauge? Pull the plunger back, insert into a 12,16,or 20mm hole and release the plunger so the balls contact the ID of the bore. I'm assuming that the C/M/F is undersized, on size, oversized. If you have a bore one of those sizes, try it out.

lg
no neat sig line

 

[The Cobbler]

^^ don't the graduation numbers go the wrong way for that tho?

 

[RoninB4]

Looked closer at the photos and my first afterthought is there aren't enough numbers on it to be a hole gauge like I have. It still seems to be a gauge of some sort but perhaps a special purpose or dedicated gauge for something. I have no idea what significance C/M/F or 12/16/20 are about. The 4 marks on the barrel may be some sort of adjustable setting for graduation range (WAG). I'd have to play with it in the shop for a while to get a clue about purpose.

 

[larry_g]

^^ don't the graduation numbers go the wrong way for that tho?

You are probably correct for direct measurement, Could be a 12,16,20 gauge gun barrel?? This guess does not account what the marks on the barrel are for. Could they be a depth from the end of the taper and the balls a diameter measurement?

lg
no neat sig line

 

[Tools4Me]

You are probably correct for direct measurement, Could be a 12,16,20 gauge gun barrel?? This guess does not account what the marks on the barrel are for. Could they be a depth from the end of the taper and the balls a diameter measurement?

lg
no neat sig line

If it is for measuring shotgun barrels, the "C,M,F" markings could be for identifying which type of barrel choke is being used. "C" for cylinder choke, "M" for modified choke, and "F" for full choke. It appears the mechanism works in the correct direction for that to be the case as well, because Full choke would be smaller in diameter than a cylinder choke would be, so the plunger would be pulled out more and the marker would be further to the right. 20 gauge barrels are also smaller in diameter than 12 gauge barrels so that fits with the markings on the tool too.

 

[RTM]

If it is for measuring shotgun barrels, the "C,M,F" markings could be for identifying which type of barrel choke is being used. "C" for cylinder choke, "M" for modified choke, and "F" for full choke.

This is the first set of replies that actually seems logical, but I can’t find the tool there using google images. Would knowing the ball diameter at those levels give more credence to your theory?

 

[Tools4Me]

After looking into it a little bit more, I think the OP does have a shotgun barrel/bore measuring device. Modern ones usually have micrometer heads, but they often still use the same three ball style measuring tip. It looks like the OP has a simple (but also more durable and compact) version of the modern tool. Probably designed that way so it can be used more easily out in the field if desired.

I attached a simple bore chart to this post which shows what the diameter should be for each shotgun gauge and choke installed. Actual measured diameters can vary a small amount depending on which shotgun or choke manufacturer you are referencing, so if the OP is in the right ballpark with each measurement I would say we have verification of the tool's purpose.

 

[mullinsrandall]

I don't know the name or anything but I have one and yes it's to check the choke on 12 16 and 20 gauge shotguns. Mine came from my grandfather. I would like to buy yours if you would sell it Mr Jeep