The special Non-Polarized socket base design allows this LED bulb to fit BOTH standard socket and also CK SCK SRCK socket. One pair of 7443 strobe light. 992, 7440, 7440A, 7440AL, 7440NA, 7440LL, 7440ST, 7440NA, 7441, 7443, 7443NA, 7443LL, 7443ST, 7443NAK, 7443-SRCK, 7443-CK, 7444, 7444NA, 7444NAK, 7444LL, 7444NAKCLCP, 7443-SCK, W21W, WY21W, W21/5W, WY27/8W, T20, etc. (For Reference Only).