Summary Keychain works for hex nuts 5/16" to 9/16". You may notice that the nut is too big when you try to use the wrench. This is by design. The nut will snap into place which ensures a strong grip. Don't worry this will not break the keychain. Buy a metal one here! Find me on: Print Settings Printer: Maker Select V2 Rafts: No Supports: No Resolution: 100 microns Notes: I used ABS