In this study, the seal bushings were designed to allow the lubricant stored in the screw and the nut system. Effect of thread clearance on the life of the screw were investigated. The screw and nut are made of S45C and HBsC3, respectively. Effects of material pairs on friction coefficient were investigated by using the pin on disk tester to simulate the friction condition between the screw and the nut. Result shows that the life of the screw increases with increasing thread clearance. The longest life for the maximum clearance can achieve 6790 cycles. Under the same surface pressure, the friction coefficients of HBsC3 on self-lubricating alloy and HBsC3 on SCM 440 are much smaller than self-lubricating alloy on self-lubricating alloy and self-lubricating alloy on SCM 440 by using nut on screw.