K+S tubing is great and its stackable (one size will fit into the the next larger one*) but sometimes its a bear to drill a centered hole into or through a small tube. Its really handy to build a jig and its an easy build. Since K+S stock is stackable, start with a SQUARE tube (pref. a bronze tube, the larger its diameter the easier it will be to hit dead center). Carefully mark the center and drill a hole. Don't be surprized if your first try is a miss, the key is to drill a centered hole thru both sides of the square tube. Once you've got a good centered hole, use this piece of square tubing as your drilling jig (use the same sized drill you used to make the holes). You can build a drilling jig with several hole sizes or just one small hole which will allow you to drill a pilot hole into the part you're creating. Its easier to drill out larger holes once the pilot hole is there. This is where the stackable part of K+S tubing really shines. One-size-smaller round tubes will fit snuggly into the next larger size of square tubes* and will hold them in place. From there, you can use a pin vice and your jig to drill perfect center holes in round tube stock and from THERE it doesn't take long to build your own custom shock absorbers, hyd. rams, axles, etc. etc.. *- Be sure to check out the handy PDF file attached to the detail pages for each K+S product. It lists what fits into what.