Cassette - Shimano (?) 6 Speed 11-21 Cassette

This was quite a little find on a low end road bike that was given to me. It was converted to a Triathlon bike by the owner and this cassette was part of that conversion. There are few markings on the cogs, only the teeth # and "index". The range is 13-14-15-17-9-21. 

It is in excellent condition. The teeth are square and without wear.

I am guessing the is a Shimano 600 AX cassette. I could be wrong. (Let me know if you know). The spacer are nylon and it looks like the pins can be unscrewed to swap out cogs. Cleaned and ready to install.