We m4a1 magazine catch part no. 75

It sounds like you're referring to the WE M4A1 airsoft rifle - specifically, part No. 75, the magazine catch.

In WE-Tech's exploded diagrams for the M4A1 GBB (gas blowback) series, Part No. 75 is usually the magazine catch button or the full magazine catch assembly (which includes the button, bar, and spring components).

• Purpose: The magazine catch holds the magazine securely in the rifle and allows it to be released when the button is pressed.

• Material: Usually made of metal for durability.