The Z bar tension wrenches are a double ended pair of tension tools. On one end you get a top of the keyway TOK wrench very similar to the short end of a pry bar and on the other you get a bottom of the keyway BOK wrench.
One wrench has a parrallel BOK tip and the other has a tapered BOK tip. The actual taper is on one side only so the straight edge is parallel with the cylinder core and the taper provides a positive grip on the cylinder profile. Personally these are my new favourite tension tools and I can see why some of the best pickers I know of custom made their own in the past. As far as I am aware these are the first comercially available tools.
Manufactured in 1mm 301 stainless steel they are made to last a lifetime