Help with screw sizes

[badgerchap]

Good afternoon.

 

My first post in several years. I'm getting back into things, and my first port of call is mounting my old mid-late 90s (the IC in the hand controller has a date of 1/30/1996 on it, so I suppose that's the earliest possible date of manufacture) Celestron C8 onto a dovetail so that I can whack it onto my EQ6. There appear to be mounting holes in just the right place for the dovetail I have (luckily) but I'm currently stymied by the size of screws necessary, as the ones currently in the holes are a few mm to short.

 

The screws are not M4. They are a very similar diameter, but a different thread count. Does anyone have any idea what they are? Likely an imperial size, I suppose, but I've no idea, having largely ignored imperial screws my whole life!

[Louis D]

How about 1/4-20, the same as camera tripod threads?  That is a pretty common size for mounting screws.  See if the screw to mount a camera to a tripod head will thread into the hole as a confirmation.

[badgerchap]

OK. I've found something that fits. No idea what they are, but that old jar of screws in the shed yielded success! Finally! 

[Mandy D]

1 hour ago, badgerchap said:

OK. I've found something that fits. No idea what they are, but that old jar of screws in the shed yielded success! Finally! 

Excelent! Just for reference, 4BA is about the closest non-metric size to M4 with an OD of 3.62 mm.

[Louis D]

They might also be 8-32 x 1/2”, 10-24 x 1/2” or even 10-32 x 1/2” screws.  I believe the first would be closest to an M4.