Black Nuts M3 x 10. Suitable for most 1.16 scale wheel axles using a 3mm thread. Can be removed using the small wrench in most nitro starter kits. Spanner or socket size 5.5mm. On 1.10 models can be used to secure manifold bolts to the engine. 5.5mm across the flats. 3mm thread size. 4.02mm tall.