This Lockmaster features 2 rollers as well as 2 hooks with anti lift pins for excellent security and weather sealing. Please note that the double spindle version is unsprung and should only be used with sprung handles. 
Operation: Lift lever or double spindle nightlatch.
Latch reversal: Undo the screw or screws (depending on the model) in the latch to remove. Reverse, reinsert and replace screw(s).