1-3/8 diameter, 7/16 bore. With ferrules and caps. Will fit all makes.
In my day ... hoop and a stick ... rolled up newspaper ... jumpers for goalposts .... zzzzzzI wonder if they put the propelling handles on the left deliberately?Seems like an odd choice to me.*shrugs*
Having been in touch with the company I can exclusively reveal that the answer is that they hold on with their right hand. A safety feature, it's better for them to use their weaker hand for going faster and their stronger hand for holding on.Seems obvious now.