Rib and truck parrels were common to 17th, 18th, and some 19th century ships. The ribs (battens) and trucks (rollers) were strung together on rope trusses. The ends of the truss were secured around the yard, while the ribs and trucks were passed around the body of the mast.
Dimension is diameter.
Brass / 5/64" / 2mm / 40/pack