Gagie's MAXIM Jar is a Hydraulic Bi-Directional Jar designed specifically for coiled tubing and conventional workstring BHAs. It may be used for fishing operations or as a contingency during drilling and milling operations. While the fish is engaged, the operator can control jar impact force ("hit") from surface by varying the load pulled or pushed on the jar before the it fires.

After firing, the jar is reset ("cocked") by stroking it back through the netural position, making it ready to fire again.

It is most common to jar a fish up the hole, however, the bi-directional feature allow the jar to be fired downwards. Reasons for downward jarring include; hammering a fish downhole, assisting in engagement of a fish, freeing a fish when in cases where it become stuck while moving up the hole, "bumping" down to aid release of a conventional overshot or spear, helping to release lock mandrels and packers which have pressure below and shearing of downhole plugs or darts.

The principle of jar impact is understood by engineers and students of science by this formula which can be used to describe the impact force imparted onto a fish:

Force = Mass x Acceleration