These are Clamp Type 6mm Aluminum Wheel Hubs by Tamiya.
Fits TA04, TA03, TL-01 and F201 chassis cars.

FEATURES: Plain silver aluminum construction (all parts).
High round cap head screws with a hexagon socket drive insert.
These wheel hubs are fastened with cap screws and prevent the 2x10mm
shaft from falling out as well as realize precise wheel attachment.
Illustrated reference guide.

INCLUDES: (4) Wheel Hubs
(5) Shafts
(5) Cap Screws
(1) 1.5mm Hex Wrench

SPECS: Wheel Hubs - Cap Screws -
Thickness: 6mm Diameter: 1.6mm
Inner Diameter: 2.5mm Length: 4mm
Outer Diameter: 12mm
Shaft Size -
Length: 10mm
Diameter: 2mm