Caldercraft Model Boat Fittings 8105TW 5mm Triple block. Walnut.
Sold In packs of 10, these triple blocks measure ((h) x (w) x (d)) 5.1mm x 4.3mm x 3.5mm and are available in walnut.
Equivalent manufacturers part number cross references:
Caldercraft 8105TW
Mantua 37100