John Guest Speedfit PSEI6012U9 Push-fit Female Connector Reducing Coupling, 3/8 OD x 9/16 UNEF, 10-Pack

I used this to install a high flow reverse osmosis water system with 3/8 inch tubing. I decided to go with a high flow RO system because I wanted to connect the RO system to a counter faucet and to my refrigerator (while receiving greater water flow than 1/4 tubing provides).I used this specialty adapter to connect my 3/8 push to connect tubing from my RO system to compression tubing (that connect to the copper piping I ran).Overall, I was flustered and unsure how I would connect my RO system to my copper piping and this saved the day. I would buy it again in a heartbeat.

Threads on perfectly with some plumber tape to a 1/4 turn shut off valve with 3/8" connections. Used this to supply water to a 3 stage under counter mounted water filtration system.

Really great product that fufils a very specific purpose. Very well made and very hard to find a compression fitting this size and style.

Amazing, just the piece I have been wanting! No more compression fittings to fiddle with! Thank you to the mfg for making this product and doing it right!

I used this to trans from my John Guest plastic tubing to the braided line and it does the trick.

Great for attaching tubing to under-sink shut-off.

Just what I needed, it also came fast. Thank you.

These fittings are so much better quality than the cheap knock off ones, I will not use anything other than John guest fittings in my facilities