Cap for motion guide apparatus

A cap for blocking a fastening member insertion hole of a guide rail of a motion guide apparatus, the cap for a motion guide apparatus comprising:

• a disc-shaped top surface portion;
• a cylindrical side surface portion hanging down from the top surface portion;
• and
• a plurality of protrusions provided on an outer peripheral surface of the side surface portion, wherein
• the plurality of protrusions is apart from each other in a circumferential direction on the outer peripheral surface of the side surface portion, and is present at an upper end portion, or from the upper end portion to an axially middle portion, of the outer peripheral surface,
• a thickness of the side surface portion between the protrusions is less than a thickness of the top surface portion,
• the top surface portion includes a center portion, and a peripheral portion thinner than the center portion, and
• the peripheral portion is thinner than the center portion within an entire area of the ring-shaped peripheral portion.