The union bonnet (Union Bonnet) and bolted bonnet valves (Bolted Bonnet) the same?
And plug valve bonnet (bolted): there is a valve cover flange, the valve cover flange is bolted and connected to the valve body, and then stuffing box.
There is no bonnet flange that is threaded directly.
Dissimilarity：The union bonnet (Union Bonnet): it is with the cap (pipe joint) direct pressure filler
