Lower Looper Screw 

Part # 544211-052

Will not work with lower looper holder # 3376839-90

Fits Singer serger models: 14CG744, 14CG754, 14SH654, 14SH644, 14SH744, 14SH754, 14SH764, all 14U Series, 14U234B, 14U455, 14U544, 14U555, 691D150GG, 691D250GG, 691D350GG, PRO4D