The 6-32 Hardened Carbon Steel Hex Lock Nut can be used in conjunction with 3.5mm screws (and US standard 6-32) to fasten components in place. These are made from hardened carbon steel and are black in color.
The Akust Hex Machine Screw Nut w/ Lock Washer - #6-32 x 1/4" - 25 Pack is a great solution to modding needs and other hardware issues that may arise. These come as a 25 pack and have a plastic container for storage of extras in the event you don't use them all.
The Akust Rustless Nylon Thumb Nut makes for easy installation and release of 6-32 screws. Use these for fan mounts or anywhere else you need easy access to mounted 6-32 mounted items.