There are 4 common fittings on lamps -
BC - Bayonet cap - standard size is approx 22mm diameter and is also known as a B22
SBC - Small Bayonet Cap - approx 14mm diameter and also known as B14
SES - Small Edison Screw - approx 14mm diameter and also known as E14
ES - Edison Screw - approx 27mm diameter and also known as E27

BC
SBC
SES
ES
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