Old Valve with left hand thread handle, why?

[ScubaBunga]

I was cleaning a bunch of valves yesterday and came across a us divers k-valve that has a left hand thread bonnet on the valve handle? I was almost ready to use a breaker bar in my vice when I noticed the notches in the nut and tried it the other way! This is on the handle and not a crossbar setup. The valve looks normal/standard from the outside - ie. the handle is on the normal side. Was this used for old doubles to remove the handle and put in a crossbar???

 

[captain]

According to my 2005 Aqua Lung valve service manual the left hand threaded bonnet nuts began in 1986 along with a change from using just a teflon stem seal to the use of the teflon stem seal and an O ring and back up ring and also involved a design change to the stem and bonnet nut to accommodate the O ring and backup ring.
Always check the bonnet nut for the notches indicating it is left hand thread, this applies to K, J and twin manifolds. The J bonnet remained right hand thread.