When printing/assmbling the Mad Cat MKII BattleMech (http://www.thingiverse.com/thing:44025), I found that the hip and waist joints were far too weak (at least for me) -- the tabs would break off just cleaning up the part (if not while removing it from the print bed), let alone trying to actually use it to connect the Mech's parts.. So, I set out to design stronger joints, and this is what I came up with. These will not break, period! In each case the "snap in" part is replaced by two halves that are inserted first, then a center piece is inserted between the two halves, forcing them to remain "full diameter", retaining them in the groove. In the case of the hip, there should be enough clearance to put the two rotator halves into the engine (one at a time); if not, the flat sides of the halves that face each other can be sanded and/or snip a little more of the lip off where it has already been flattened to increase the clearance enough to fit them in. The insert (that has the pins that connect to the leg) snaps into the two rotator halves, keeping the halves apart and retained in the engine. For the waist, the "bases" were tight enough for a friction fit (no glue); same procedure, put the two halves into the upper joint, then put the insert between them; then press the engine onto it. You may need to sand or scrape the joint or square recess it sits in depending on your print, and how well the support material was removed from the engine. NOTES: I printed the original model at 3500%, so the size of these parts is based on that; you will need to scale these appropriately to match the scale you printed the Mad Cat in. After printing the first hip joint, I adjusted things slightly to make the pieces fit together better; since I had to do some sanding on the rotator flat sides (to make more space between them, so they'd fit in the socket), and trim the insert to fit (it was too tight). The second hip I printed still needed some cleanup to get it to fit (I didn't adjust by enough). I also found that the second hip is slightly trickier to fit the insert into because you cannot hold the rotators in position from the backside; but I got it in; very nice results.Print two of each "half" parts (they're symmetrical). And one insert. Print two sets of the hip parts for two hip joints; they are also symmetrical, so different parts are not necessary. The rounded-off part of the leg connection should face up (allowing the legs to move further "outward" vs. under the Mech. The waist halves are intentionally printed "on their side" so that the sheering force will be perpendicular to the print layers, making it virtually impossible to snap off the "tab". To install, first insert the two halves one at a time (you may need to trim off a little bit of the "lip" that fits into the rotation groove in the engine part in order to get the second one inserted. The idea is that the amount of "gap" provides enough clearance to insert the second one once the first one is slotted in the rotation groove. Once the two halves are in place, insert the the center part, which forces the halves to remain separated, preventing them from slipping out of the rotation groove. The waist joint works on the same pricipal; insert the two halves, then force the center piece in to "lock" the halves into the joint. The files named "visual reference" are there to show what the combined part should look like when installed, and are not meant to be printed.