Caldercraft Model Boat Fittings 8106SN 6mm Single block. Natural.
Sold in packs of 10, these single blocks measure ((h) x (w) x (d)) 6mm x 2.9mm x 4.2mm and are available in natural boxwood.
Equivalent manufacturers part number cross references:
Artesania AL8514
Caldercraft 8106SN