3/4 dia. With 3/8 dia. Hole for TT Grahams,etc.
Used on the small, (4-4 1/2" toys) Hubley Studebaker and Airflow chassis, Use the #12 7/16" wood hubs on Hubley toys
Also used on Dinky, AC Williams, Slush, Kenton, and others
Sold as a set of 4,
Refer to page 8 and 14 of the Thomas Toys catalog