Caldercraft Model Boat Fittings 8103DW 3mm Double block. Walnut.
Sold In packs of 10, these double blocks measure ((h) x (w) x (d)) 3.6mm x 2.9mm x 2.4mm and are available in walnut.
Equivalent manufacturers part number cross references:
Artesania AL8524
Caldercraft 8103DW
Mantua 37050