Spring dividers

[ED65]

Would anyone with an old 6" spring dividers mind measuring the maximum width it'll open to please?

I managed to pick up a nice old one for very little last weekend from a rare maker in this part of the world, Athol Machine Co. of Athol Mass. which may mean it dates to before 1921. Sorry no pics, camera is on the blink, but it looks like every rusty, blunted, old spring divider you've ever seen so nothing new to look at.

It was seized when I got it but the threads looked in good enough nick under the rust that I wanted to take a chance on it and I managed to free it just doing a surface cleaning, but I'm not sure if it's working freely through the entire range of motion as I've never handled one before. Pics online have been no help as invariably they don't show the knurled knob screwed all the way out on the threaded rod!

 

[Cheshirechappie]

On mine, maximum is 6 1/2". That's on a (relatively) modern pair by Moore and Wright.

 

[Bm101]

Same here. 6 1/2"
2"between the 'set screws' if that's the right name. Threaded rod is 2 1/2" to the thread adjuster at full extension with the ball (stop) extra if that makes sense.
Moore and wright also.

 

[ED65]

Ta gents. This one will only open to about 45-50mm and I suspected it should open a smidge more than that! Presumably the right 'turret' needs to rotate but is seized so I'll hit it with some penetrating lubricant and leave it for a day or so.