Caldercraft Model Boat Fittings 8105DN 5mm Double block. Natural.
Sold in packs of 10, these double blocks measure ((h) x (w) x (d)) 5.1mm x 2.7mm x 3.5mm and are available in natural boxwood.
Equivalent manufacturers part number cross references:
Artesania AL8521
Billing Boats BF698
Caldercraft 8105DN
Corel AMNB115
Mantua 37061