This is a holder for Jumperwire, you can drill or add some holes to mount. I have mounted my holder with double-sided tape, but you need very strong double-sided tape, mine has detached from my magazine, so I will drill holes and mount it with screws.
It has 20 slots with a width of 2mm in a interval of 5mm.
The holder is 145mm long and 38mm wide.
Mine is made of black PLA with a diameter of 1.75mm.