The 859 series features split spindle nightlatch operation. Type 17 refers to the 2 hook, 4 roller version of this lock with 1510mm between the outer rollers.
Operation: Lift lever or split spindle nightlatch.
Latch reversal: Undo the screw in the side of the lock case adjacent to the latch. Remove the latch, reverse, reinsert and repace the screw.
Night Latch reversal: Insert the split spindle 2/3 of the way in on the internal side and 1/3 of the way in on the external side