They are called "end fasteners"
Part numbers are 3381 for ones with the 1/4-20 screw included.
3378 with no screw.
Those are 80/20 part numbers not Mcmaster
I suggest calling your local 80/20 distributor and support your local economy... Forget McMaster. I work with the local distributor in Minneapolis.
www.8020.net will help you find a distributor in your area.
Hope that helps...
Ian