Fuel gasses have L/H threads but LPG appears to be parallel and Acetylene appears to be tapered .
They will start into each other but not far enough to seat the rubber seal.
The outlet is different as LPG uses R/H for this but Acetylene is still L/H.
I Remember a few years back I bought an LPG torch at the local cheapo tool store but it ended up having a weird thread on the inlet , I ended up having to go to a gas specialist store to get a hose made and then found out it needed an adjustable regulator as the generic BBQ unit I was hoping to use had too much juice .
By the end of that saga it ended up costing more than a name brand unit that came with a hose and regulator 
They say you live and learn !
I did a lot of living that day !
Ian