Installation in M16 threaded hole on the top of the housing. Please check compatibility with a specific housing. Compatible underwater strobes: Inon S-220 / Z-330 / Z-240, Sea&Sea YS-D1 / YS-D3 Mark II/ YS-D3 Mark II/ YS-D3 DUO, Retra Pro MAX (including HSS), Marelux APOLLO III V2.0 (including HSS), Marelux APOLLO-S (including HSS).