Well, I'm not sure what a Z59 tailcap is, but I've tried the DX boots in SureFire Z57 and Aleph E series tailcaps. I got the assortment SKU 5498 and the blue 7321. All need the post inside cut off to play well with the SureFire/Aleph switches. The blue boots are very flexible, the other colors less so, but all are more flexible than a typical Aleph boot. The blue boots are a little shorter in height and may, or may not, play well with clicky switches. The shorter boot can sometimes keep just enough pressure on the switch post to keep it from turning fully off.