Special Strut tools

I'm replacing my struts front/rear. I saw that there is a special tool that will hold the strut piston shaft so you can remove one of the nuts on the piston shaft.
What is the part number or generic tool that can be used and who has it for sale?

Use an allen wrench with a pipe on it. To do that you have to make a strut socket by grinding flats on a socket that fits the strut nut. Then you can use a big crescent wrench on the socket. Plan B is to hammer it with an air gun.

For strut nuts, I've always used an air gun when available. If that doesn't work or is unavailable (mobile work), large vicegrips on the shock pin usually hold it enough. Rarely do struts get removed if they're going to be used again, so no worries about damaging the seals. Put anti-seize on the new nut to prevent it from rusting too tight.