Hi I had a question on using the pneumatic cylinders.
My team is currently using them with single acting solenoids, one being active close, and then being rubberbanded open.
The question I have is is it absolutely necessary to plug the other cylinder fitting that’s not being used? if so how would I do that?
You want to leave the pistons fitting open. Otherwise it would try to hold your claw open. If it was sealed the air would act as an air spring.
Kudos for actually calling these things “cylinders” rather than pistons! While most in the forums don’t seem to care, I think our students are done a disservice by not learning industry-standard terms.
Now about the plugs: The unused fitting in the pneumatic cylinder is indeed left open. In industry, we would at least screw in a muffler to dampen the sound (big cylinders are noisy) and to keep it clean inside, but these are not legal vex parts 
On the solenoid, however, if you are using a double acting solenoid to run a single acting cylinder, you’ll need to plug the unused output port. You can choose what port to plug, based on whether you want pressure in the inactivated state or the activated state (this is the advantage of running dual-acting components as single-acting). A plug can be made by heating a piece of tubing with a heat gun while pulling/stretching/twisting it to seal it closed, or you can buy plugs like these: http://www.smcpneumatics.com/KQ2P-04.html which were included in pneumatics kits years ago, so should be legal by the “grandfather” rule.
We’re actually doing the opposite. We’re using a single acting solenoid to run a double acting cylinder.
So our tubing runs from the solenoid to the cylinder fitting closest to the thread. Would we keep that other cylinder fitting open?
Yes, the exhaust port on the cylinder stays open to the atmosphere.