That is a fishing tool for a GS type or style blanking plug used in oil and gas wells. It has 3/4" or 1" sucker rod threads on top and is ran downhole through the production tubing to latch onto the blanking plug which is usually set in the profile nipple. The tool threads on to the sucker rods and is ran downhole on a pulling unit. Some brave rig hands have actually ran these on the sandline to fish out the plug. There is also a similar style tool manufactured by Frederick's Machine put of Louisiana. I believe it's listed in their catalog as a GS pulling tool. Can be run off wireline, slick line or sucker rod. Some companies call it an X-lock, it just depends on the manufacturer. Every manufacturer of blanking plugs or standing valves have their own running and pulling tools.

That is a fishing tool for a GS type or style blanking plug used in oil and gas wells. It has 3/4" or 1" sucker rod threads on top and is ran downhole through the production tubing to latch onto the blanking plug which is usually set in the profile nipple. The tool threads on to the sucker rods and is ran downhole on a pulling unit. Some brave rig hands have actually ran these on the sandline to fish out the plug. There is also a similar style tool manufactured by Frederick's Machine put of Louisiana. I believe it's listed in their catalog as a GS pulling tool. Can be run off wireline, slick line or sucker rod. Some companies call it an X-lock, it just depends on the manufacturer. Every manufacturer of blanking plugs or standing valves have their own running and pulling tools.

References:

http://www.fredmach.com/wireline/2321763