Some time back someone wanted to find tree steps much sturdier than the usual hunter screw in type. He should go to a farm store and look at the screw-in farm gate hinges (pivot pins), These are 1/2 - 5/8 screws with an upturned end to drop the gate hinge on. Availiable in various lengths, should be very strong since they hold up heavy gates. Also availiable in very long lengths for bolting completely thru gate posts, but probably not as useful since they are machine threaded for a nut not wood threaded for screwing in.