subs can be kept on hand for various needs that may arise the fishing neck 3 has been modified by removing some material to allow the bypass belt 5 to fit over it but such modification does not prevent the use of the fishing neck 3 without the bypass belt 5 in any manner in which a fishing neck could normally be used the above described embodiment in three pieces is preferred because it is easy to manufacture versatile and makes use of standard components however there is no reason why the coupler could not be made as a single piece that is the bypass belt 5 could be an integral part of the fishing neck 3 such a one piece coupler could either have screw threads to receive a rope socket or contain an integral rope socket with means for holding the wireline that are well known in existing rope sockets of various types the lower end of such a one piece coupler would have screw threads which might fit directly to the perforating gun or other oilwell device such as a collar locator or such screw threads could connect to a sub if an adaptation between incompatible screw threads is ever necessary the essence of the present invention is expressed when the coupler has any means typically a rope socket for being connected to a wireline and any means typically screw threads for connecting to an oilwell device such as a perforating gun and channels to allow gases and fluids under pressure to bypass the coupler fig3 shows a cross section through the coupler at the bypass belt 5 which covers the reduced region 12 of the coupler the inner hole 16 extends through the entire coupler from the fishing neck to the downhole end.