I believe that you're describing the clutch release bearing.
Hi I was wondering if anyone could help me out with the last part of completing my rebuild, i don't know what the part is called but il try and explain
when you seperate the gearbox from the engine there is a (think) plastic bearing kinda thing that goes onto the shaft which goes in to the clutch, what is this black plastic thing and how do I find out if it's broken? Oh and it's in the bell housing
Dan
I believe that you're describing the clutch release bearing.
thrust bearing or clutch release bearing like the man said