Our GC Valves are currently on backorder,
we are currently using a very well made Italian valve.
These Italian valves are equivalent to the GC 350s in quality.

If you order the GC 350s we will ship the new Italian valves.
They are only available in 1/2", we carry fittings that have 1/2" thread and accept 3/8" air line if you want to use 3/8" line.

This valve is pretty cool.  It's a 3-way valve meaning it can operate a pair of bags for Front/Back applications or just one bag in F/B/S/S applications.  It is clean and eliminates fittings that would normally be used between the fill and dump valves, so fewer places to worry about leaks.  It's rated at 450 PSI and has a huge 3/4" inner orifice.