The Push Pogo Pin 4 - Cup Tip is normally used for electronic JTAG uses, but they can also be used for bots. The cup on the trip would be ideal for receiving a pin of some sort.
The cup measures 1.5 mm (0.059 inches) in diameter, the outer shaft diameter is 1.01 mm (0.040 inches), and an overall uncompressed length of 33 mm (1.3 inches) with 6.5 mm (1/4 inch) travel.