SK25 is the vibratory media kit or commonly referred to as a starter kit for the Model 25 vibratory machine.

Also recommended for the M40.

The SK25 includes the following:
150 pounds of AC3S50A 5/8" x 1/4" - P-20 ceramic media
1 gallon of BKS-60 (048) vibratory compound
1 gallon of AR-60 (047) vibratory compound