I recently switched everything in my shop to the Oetiker 3/8" Swing Coupling.
Found best price here for about $20 each but I can't find them on their site right now.
http://www.industrialsafety.com/Oetiker Catalog:
http://www.wescoproductiontools.com/wp-content/uploads/2014/01/ATP-SwingCouplerCatalogue.pdfThen bought Milton 3/8" H style plugs (for all my tools) to go with them from
http://www.tooltopia.com/MIL1837 $1.43
MIL1838 $2.44
MIL1839 $1.49
MIL1840 $1.49
Obviously their are lots of choices and styles of fittings to choose from. After my own research decided on the above combo because the couplings are very well made and there is no obstruction to air flow, you can look straight through the coupling and plug. Additionally they work with common Milton plugs, so very affordable and easy to get more when you buy more air tools. I went with 3/8" for everything, and you can get the plugs with the 1/4" NPT to use with your blow guns, die grinders and whatever else you may have had 1/4" fittings on before. Another advantage of this plan is if you don't always need the fancy Oetiker coupler for flow you can use a standard/cheaper Milton coupler with your same plugs.
All together I spent $200 total for 5 couplers and 55 plugs.
This setup flows a lot more than the common size couplers and is great for impact wrenches and other tools that use a lot of air. The couplings are also not very bulky, so I felt worth the higher flow for everything in the shop and not worth having two sizes of couplers and the confusion and frustration that can cause.
Even if you don't swing for the Otiker couplings... I'd recommend the same 3/8" H style plugs and the standard Milton brand couplings that fit them. like I said I use some of those Milton couplings on lesser used or less demanding things, but they're still fully interchangeable with everything in the shop. And either kind of coupler in this style/size flow plenty for most anything I can imagine needing/using, plenty of overkill.
Grigg
