Lamp caps and holders together with gauges for the control of interchangeability and safety Part 1: Lamp caps (Incorporates Amendments A1-A3: 1995@ A4-A6: 1996@ A7: 1997@ A21: 1998@ A22-A23: 1999@ A24: 2000@ A25-A27: 2001@ A28-A30: 2002 and A31-A32: 2003