Trem Arms

Some Strat Copies (Including Squiers) can have either 5mm or 6mm threads.
You can always check by trying either a 5mm or 6mm thread bolt/screw in the thread.

(Fender USA Strats have a different thread 10/32" - so for these models make sure the arm is for USA models).

*Tip - screw-in arms often benefit from a some PTFE tape around the thread to help compensate for thread wear in the block (PTFE is an extremely thin tape used for pipe joints).