ACS Paws M30 Freewheels M30x1.0
ACS has set the standard for freewheels for almost 2 decades. Stronger, less expensive, and easier to replace than cassette hubs. The M30 has a black center ring, with a nickle plated sprocket ring. Fits 3/32" or 1/8" chains. 
Features
1/2 x 3/32 or 1/2 x 1/8 chain compatible
Cold forged chromoly construction
12 Degree engagement angle (30 steps total)
Nickle plated sprocket ring
Fit only 30mm small hub bodies
Uses a 6-spline removal too