Made by Fox, this set up can be used as a semi-fixed bolt rig or as a running rig depending on where you position the main run ring.
The main run ring can be pushed into the recess to become semi-fixed or the main run ring can be left to slide as a running set-up.
This set-up can also be used as a semi-fixed set-up without the main run ring, but using the notches on the rubber to hold the swivel on a lead in position. The tubing, in this case E.S.P. sink link, which sinks the mainline in the feeding area and prevents tangles.
Added by Julian;
In semi-fixed bolt rig mode, the above rig is ideal for when you have confident feeding fish and you want the hook to prick/penetrate as soon as the fish picks up the bait, as the principle behind the bolt rig is that when the fish picks up the bait, the resistance from the weight of the lead causes the hook to set.
Alternatively, in running-rig mode, you are allowing the fish more room for manoeuvre before the weight of the lead takes effect. I have used this method to great effect on waters with shy feeding fish, and in particular on waters where I’m fishing at distance and I want improved indication to avoid fish picking up the bait and kiting to the left or right without registering a take.