If it's designated AP that should be Accushift Plus, as opposed to Accushift. It came out in 1990 and incorporated revised gate cuts and profiles to improve shifting under load. Basically, it was a response to remain competitive with Shimano's HyperGlide cogs. I'm aware of at least two levels of AP frewheels. There was a WT series used on Superbe Pro and Sprint and an AL series used on all the other lower groups. Both came with silver cogs though there were also more economical versions of the AL series with dark brown/black cogs. Sorry, but I don't know the exact nature of the techincal differences betwen the two series.