Having trouble trying to find these connectors,
OD is 8mm, there's a 2 mm center pin in this like a standard 5.5mm/2.1 (female),
ID is about 6mm.
No ebay, etc. for this specific size.
It's the same plug shown on this ebay listing for a charger.
https://www.ebay.com/itm/42V-2A-Power-S ... 2417530488?