after read other review , I be concern this would be difficult to assemble . maybe they have improve the instruction , but I find it very easy to put together by read the instruction . I think there be two key to make it go smoothly . 1 . do not fully tighten the screw at first . they should be just loose enough to have some room to move to get everything in place . once it be assemble , then tighten everything down . 2 . use a socket wrench with a ratchet . use the hex wrench to hold one side in place and use the socket wrench to tighten . the proper socket size be list in the instruction , but I think it be 9\/16 '' . it only take my about 30 min . to get it fully assemble from the time I open the box . it have be a huge improvement when do p90x to put the dumbbell in easy reach to adjust and pickup to minimize down time between set and avoid risk of injury from pick they up from the floor each time .