Hello everyone! I am designing a sort of automatic spring gun to use with projectiles the size of normal tennis balls - sort of like a bowling machine. I have a horizontal spring, attached at one end to a square sheet of metal, and fixed at the other end. The square sheet of metal is supposed to hit the 'bullet' when the spring is freed after having been compressed. As a constraint to allow for movement in only one axis, there are four holes in the square sheet around the spring, and four fixed shafts to go in them so the sheet can only move forward or backwards. The only problem is, I need something which will connect the square sheet with the shafts in such a way so as to allow lateral movement of the square sheet caused by the spring, with minimum friction. A picture is attached: Are ball bearings alright? Is there anything less complex? Preferably I need something that I can mount onto the sheet. I'm a complete beginner when it comes to mechanical components... Any help would be appreciated.