These are the piston ring compressors that we use here at ATS. The concept is simple..it's just a tapered cylinder that compresses the rings and you push the piston/rod assembly into the block. Because the pistons is dropped straight in the rings have no change of rotating out of place like they do with the expanding band style compressors. The save time and headaches. They will work with all brands of stock and aftermarket pistons, but they are size specific so order based on your new piston size.

Tapered Ring Compressor Sleeves

• Made from sleeve forgings to offer the same toughness as Wiseco's forged pistons, these tapered ring compressor sleeves are hard-anodized and Teflon®-coated for low friction and prolonged wear resistance.
• The sleeves have a smooth radius that tapers down to the specific bore size, compressing the piston rings smoothly and evenly.
• These sleeves greatly reduce the difficulty of installing thin, high performance oil rings. Tapered Ring Compressor Sleeves

  This video shows to to use them: http://www.youtube.com/watch?v=PbbPXuwDYfE