Piping insulation? its a big tube of foam plastic
there are a few different accessory overload options that add a bit more tube on a T bracket .
most bars are about 7/8~15/16 to .. 26mm, oversize 1.25" in the middle .
I have 2 stems stacked on My threadless steerer the tube one is for my Bar bag mount, but once you fit it,
the cross bar can have room for a lot of gadgets, just needs to be a little longer.. .
I believe there is a Handlebar mount for wristwatch stuff made as a tidy product ,
by one of those heart rate monitor companies if you want a tidy special made thing.