Installation is not easy because of the flat bar for actuating the lock. The instructions are sorely lacking in this regard. One end of the bar has two "dimples" which must go into the combination side of the lock. There are 2 different lengths provide. I found that neither one worked for a 3.5" install and the longer one had to be cut. I cut it too short and did not have a working one because I inserted it the wrong way around. I ordered a replacement unit rather than try to get the part from tech support. Good thing I did too because the original one would not stay open fully, but "rebounded" about .5 inch not allowing the gate to close fully. However once I replaced the combo side3 of the lock with the new unit, it worked. I also rebuild my gate with 2x6s laid with the 1.5" side to mount the lock so that was room for the mechanism without having to add a block.
Alain 
