are passable through tool 10 are fixed by design during manufacture by the length of the helical track 42 and the keyway 56 this is not to say however that this maximum number of plugs is the only number of plugs that will be passable before a plug is denied passage rather because the key is placable in the keyway 56 as the tool is being run into the hole at any point on the helical track 42 that is exposed to the keyway 56 any number from the maximum number down to a single plug may be selected more specifically the key 52 is a component of the tool 10 that is removable and replaceable at any point along the keyway 56 where the helical track 42 crosses the keyway 56 the helix sleeve 40 itself may be marked to show how many plugs will pass before denying passage to make it a simple operation in the field for a rig worker to place the key in the keyway 56 to select a number of plug passages to facilitate a particular operation it should be noted that because of the high pressures generally encountered in the wellbore for operations related to seating plugs and the potential operations that might be effected by pressuring up on such a plug for example fracturing at about 10 000 psi the key 52 should be robust in size and construction as it is in the end the key that stops movement of the balance of the components another feature of the tool 10 is that if for any reason after plug passage has been denied it is necessary to pass the denied plug the follower s.