This is a noise supressor/muffler for the intake on certain models of Craftsman and Porter-Cable oil-less compressors. Specifically for compressor heads that use filter/intake part #CAC-1371 or similar (see images). This design is also only meant to be used with a flexible plastic like TPU or similar. You need it to be flexible for a snug slip fit over the stock assembly.

The specific compressor I designed it for is an older Craftsman 30 Gal. upright, model 919.167310, onto which this suppressor fits perfectly under the compressor shroud. This should fit many other similar compressors of this style as well. This will cut down on the harshness of the compressor intake noise and reduce the loudness very small amount. Do not expect that it will make an oil-less compressor quiet. For that you need to do a lot more than this.

To install, remove the shroud from your compressor. You can use the stock foam (sponge) filter by pressing it into this suppressor's inner ring and then press it over the intake fully.
OR
You can use a roughly 3" (75mm) dia. disk of thin filter fabric that air flows through freely. I used a synthetic (rayon?) filter fabric. The type often found wrapping tubular charcoal water filter cores (where I got it from). Hold the disk of fabric in front of the stock intake and press this suppressor over it ensuring that the edges of the fabric get sandwiched into the groove all around the circumference.

It's a snug press fit and should not easily pull or vibrate off. Test that you get enough air flow through it. Replace the shroud! Don't run one of these compressors without the shroud for more than a short test as it is integral to the air cooled design and they get really hot, really fast.