I dont know what the bar/rod of metal that attaches to a clevis pin and pushes into the master cylinder is called

could anyone tell me what its called and also what size clevis people used.

I woudl have searched but not knowing what its called makes it difficult

It's a master cylinder pushrod. As for the dia it will depend on which m/cyl....

Girling Master Cylinders. use a 5/16 UNF thread.

apologies its a sierra master cylinder