Finding the angle on a small piece?

[dvddvd]

I'm wanting to find the angle of this piece of metalwork. It's a part for a headless guitar and need to cut the guitar neck end so it fits perfect.
It's only 25mm x 15mm.

Is there such a thing that I could slide in to measure it? Then transfer it to a mitre saw? The sliding t square things all see to big? Thanks

 

[Fred48]

Get a piece of wood around 3" x 1" PAR ( machined planed all round) about 12" long or longer. Ensure the edge that is going to fit against the mitre saw fence is flat.
place the piece of metal against the long edge of the PAR. and Mark the angle with a marking knife.
Cut on the mitre saw. It then will need 'tweeking' on the mitre saw until you get a perfect fit.
Fred

 

[Jake]

Looks like you can simply take the angle from the outside with a bevel gauge etc (not sure what angle measuring devices you have).

Or put some card under the prong with the (straight) edge pressed up against the body of the thing, draw a pencil line along the inside of the prong. Remove, extend the line with a rule, and use a protractor.

Edit: Fred's method is even more direct.