Hayward SPX0540Z4A No 40840 Hex Nut with Washer Replacement for Hayward Underwater Lights Hex nut replacement Fits hayward starlite series underwater lights models sp0540, sp0541, sp0542, sp0543, sp0550, sp0551 Also fits hayward u l junction box, anchor socket models sp0680, sp1392 Weighs 5.4-Pound