Towbar spindle hole: 12mm (not included). Spindle material: 20CrmnTi, carburizing heat treatment.Feedback is very important to us. It is impossible to address issues if we do not know about them! Faction is our ultimate goal. We work hard to earn your trust and future business. A If you receive a defective item, you may return it or ask for a discount. Due to time zones, our reply to your questions may not be immediately. If it's non-workdays, please kindly be patient and wait till Monday.