I have some sandpaper that my brother in law gave me (he's a mechanical engineer specializing in materials), and I told him that I'm getting into straight razor restorations. Since a lot of this is right up his alley he's been quite interested.

Anyhow, he mentioned there are two different grit number systems (European and American I believe he said). In particular, he gave me some silicon carbide that says "1200/4000" and another that says "P1200". The 1200/4000 stuff is significantly finer than the P1200 so I presume the P1200 is using the same system as the 4000 side of the 1200/4000, whatever that is.

My question is what system are people using when they talk on here, because I've only ever seen single numbers given.