Switch - Marshall - Toggle, latching 2 position DPST, On-Off, Chrome Tip.
15A 250VAC rating. Used for Mains and Standby switch in Marshall 1959SLP, 1987X, 2245 and others. See Marshall Nut S-HM300N if necessary. Nut sold separately.
Note: On-Off switches may sometimes be referred to as On-None-Off.