Handles vary in design but it may be that the earliest was a simple L format – perhaps the originals were even made by bending the latch shaft – all we know is that this type of opener is still very popular in all areas of industrial activity.
Many have tabs or cams to latch with, while others have square drives to fit two or three way latching mechanisms. Either can suit multi-point rod locks – for which the L handle design is excellently suited as it gives perhaps the optimum degree of leverage.
