Lampholders bases come in various different styles, if you are not sure what style you need then check out below for their explanations.
10mm - 10mm Entry lampholders are the more popular entry lampholder to fit on any 10mm fixing point, the lampholder as it comes should not be used for a hanging light fitting. However you can add a 10mm cord grip to enable you to hang this form a cable.
1/2" - This lampholder entry is the same as the 10mm but this has the 1/2" 24tpi entry thread, you will find these generally in older style light fittings. Again the same applies you cannot use this when hanging from a cable unless a cord grip is being used.
20mm - The 20mm lampholders are designed to be used with 20mm electrical conduit systems and will screw directly onto a threaded piece of galvanised conduit pipe.
Pendant -The pendant style lampholder is one of the most popular lampholders we sell to pubs/restaurants and retro fitting in domestic dwellings, these have built in cord grips so perfect for creating stunning pendant style light fittings.
Batten - Batten lampholders are very popular with theater companies for lighting around stages and Hollywood style mirrors. These lampholders have flat discs fixed to them ideal for fixing the lampholder to a wall of ceiling.