This is the Du-Bro 601 4-40 Spring Steel Kwik-Links

Spring Steel Kwik-Links are the tried and true top quality Kwik-Link. Ideal for control linkage hook-up. Use with threaded rods or threaded couplers. 2-56 are for use with .072 dia rods, link guards included. 4-40 are for use with .093 dia rods, spring keepers are included.

Solder Kwik-Links are nickel plated making a strong, attractive and easy to solder connector for servo or control horn. 4-40 are for use with .093 dia rods, spring keepers are included.