LEGOTechnic NEW LIGHT GREY RACK GEAR SET Track Kit 1x4 Part Piece brick Mindstorms NXT robot robotics assortment pack ev3 motor (Pack of 10 pcs)

My son said they worked good.

Worked. Minor recommendation: add the four digit Lego item number to the title. This helps custom quickly identify the item. It took me a while to measure the dimensions and count the number of teeth to confirm this is correct piece I want.

This was a gift.

Don't work