If you've seen the video, then you understand. These are the kind that use rope, not chain. you are likely using plastic so you want as much weight shifted towards the outsides as possible and chain is heavy. Though if people want chain I can make them for chain. http://m.youtube.com/watch?v=SncapPrTusA&desktop_uri=%2Fwatch%3Fv%3DSncapPrTusAGo on solidworks, sketch and extrude a 12-14+ (these are 14" long) polygon. Then select the top face and chamfer it all the way down, so if it is 14" long, set the chamfer to 14". This will taper it, since tapered ones are more powerful and easier to control. The chamfer angle should be about 1.6-1.8-2 (these are 1.8 degrees taper) and this is my preferred range because it isn't too crude, like a baseball bat, nor is it too delicate so that it makes no difference. I think that the taper is "polite" but effective. At the base these are like 1.3-1.5 inches wide. but I was already planning to taper them, so do as you wish. Once the taper is set, select a face and sketch a circle, this should be about .5" - .2" in diameter, depending on how strong your material is and how thick you make them. Select mirror entity/sketch and select the circle. now you will be set to extrude-cut the two rope holes necessary for tying it all together. Finally, find the centerpoint of your top surface (if you have a difficult polygon like my heptagon here just set measuring lines 90 degrees from each face and just bring them across to the other end of the face, and repeat until you have several lines all pointing toward the same point - the center of the face.) Anyways find the center and sketch a circle or polygon (circular or more than five sides is better - I used a nonagon) and then extrude-cut it out so that you have a shaft from the top face right down into the upper of the two horizontal tunnels! Now you can thread a rope/ropes/ whatever in through the top, then down and around through the holes so that you get a secure, centered, balanced chuck pair. Print multiples of this item, obviously you need two limbs per chuck, and of course you wanna be Bruce Lee so you a chuck for each hand. So four in total. Follow the law, do the right thing, do what is right. If you can't have them where you are, don't print them, but many many locations do allow them, so in those places, have fun. I got my inspiration from traditional polygonal chucks everywhere, the stringing videos from erniesbudolab on Youtube, Lee Barden and His designs which He demonstrated on Youtube (I recommend you buy His Ironwood Prochux definitely), Woodall's custom Workshop and their chucks - Go there and buy the best chucks you could want) And finally, the chuck freestyle wiki.