For TRX4 TRX6 ONLY, NOT fit other Crawlers. Extending the track width for greater control and stability Hex Size:12mm, Hole Diameter:6mm The Spacers made of quality Brass, add weights to wheels, lower the gravity and improve stability. CNC machined for precision. Increased strength and precision. Easy upgrade from the part. with these Hex hub hub extenders, you can Extends the distance of the wheel, giving you better control over your RC car on rough terrains,improving your driving experience. Specification: 15mm Material: brass colour: As shown Package Contents: 1 x RC Brass Spacers Wheel Extenders Kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.