The aluminum piano hinge i purchased is 4" open meaning when laying flat it measures 4". The pin diameter is 1/8" and the leaf thickness is 1/16". The knuckles are 1/2" long each. I purchased my piano hinge from Mcmaster.com not sure if they ship to residential or not, its a business supply store. I was able to have it shipped to my job as they order stuff from there frequently.