A much smaller 'Pin' connector that is used exclusively with small LEGO wheels. (Larger wheels use Technic Pins and Axles.)
The small 'Wheel Pin' connector is extremely similar to the Technic Pin connection, but it is only about 2LU (3.2mm) wide and 3LU (4.8mm) long.
That's 1/3 narrower and 2/5 shorter than a Technic Pin connector.
 | 1×2 Plate w/ 1 Wheel Pin 21445 |
 | 2×2 Plate w/ 2 Wheel Pins 4600 |
 | 2×2×⅔ Plate w/ 1 Wheel Pin 67688 |
 | 2×2 Wide Plate w/ 2 Wheel Pins 6157 |
 | 1×4 Plate w/ 2 Wheel Pins 2926 |
 | 2×2 Plane Holder w/ 2 Wheel Pins, Bottom 4870 |
 | Tilt Steering Axle w/ 2 Wheel Pins 69964 |
 | 2×4 Tilt Steering Holder 69963 |
 | 2×4 Brick w/ 2 Wheel Pins, Cutout 18892 |
 | 4×7×⅔ w/ 4 Wheel Pins 2441 |
 | 6×10×1 Vehicle Base 65202 |
 | 4×10×2½ Vehicle Base 12622 |