Seldén double blocks for dinghy purchase systems, mainsheets and control lines, available in standard ball bearing (BBB), high load ball bearing (BBB25) and soft attachment (S-series) versions from 20 mm to 60 mm sheave diameter.
How to choose
A double block carries two sheaves in a single body, making it the core component of any purchase system. Whether you are building a mainsheet tackle, a kicker, a vang or a control line purchase, the double block is where the mechanical advantage is created. This collection covers three types: standard ball bearing blocks (BBB), high load ball bearing blocks and soft attachment blocks.
Standard ball bearing blocks use stainless steel ball bearings and glass fibre reinforced polyamide sheaves. They suit the majority of dinghy and keelboat purchase applications and are available in four sizes. Choose the size to match your line: BBB20 for lines up to 6 mm, BBB30 for lines up to 8 mm, BBB40 and BBB60 for lines up to 10 mm.
The BBB25 high load block is a specialist option with an all-stainless construction rated for wire and rope up to 5 mm. It is compact but strong, suited to halyards, tackles and applications where load is high relative to line diameter.
Soft attachment blocks (S20, S30, S40) mount with a Dyneema lashing rather than a shackle. They are lighter, eliminate metal-on-metal contact at the attachment point, and reduce snagging points on deck. The S20 double accepts lashing up to ø4 mm. The S30 double takes 2 mm Dyneema lashing, not included. Soft attachment versions suit applications where saving weight and keeping a clean deck profile matters.
The becket variant adds a fixed attachment point on the block body where the standing end of a purchase system is anchored. If you are building a 2:1 or higher purchase you need a becket on the double block. If the standing end is anchored elsewhere, the standard version without becket is sufficient.
The BBB60 double is the only swivel-mounting double in this collection, suited to mainsheets and sheets on larger dinghies and keelboats where the lead angle changes and a fixed attachment would create misalignment.
What's in this collection
The BBB20 ball bearing doubles cover lines up to 6 mm and include a standard double with stainless strap (402-101-03R), a becket version (402-101-04R) and a through-deck lead double that mounts with 2xM4 screws (402-101-18). The S20 soft attachment double (402-101-61R) uses Acetal sheaves with stainless ball bearings and accepts lashing up to ø4 mm.
The BBB25 high load doubles cover wire and rope up to 5 mm with all-stainless construction and ball cages to reduce friction and weight. Available as a standard strap double (402-201-08R) and a becket strap version (402-201-09R).
The BBB30 ball bearing doubles cover lines up to 8 mm and include a standard double with stainless eye (403-101-04R) and a becket version (403-101-05R), both with glass fibre reinforced polyamide sheaves and Acetal bearing cages. The S30 soft attachment double (403-101-61R) uses Acetal sheaves with stainless ball bearings; 2 mm Dyneema lashing is recommended but not supplied.
The BBB40 ball bearing doubles cover lines up to 10 mm with a fixed stainless eye, available as a standard double (404-101-06R) and a becket double (404-101-07R). The S40 soft attachment double (404-101-61R) has two 40 mm sheaves with stainless ball bearings for dynamic loads up to 10 mm.
The BBB60 double swivel (406-601-05R) has two 60 mm sheaves with Delrin ball bearings for high dynamic loads up to 10 mm line. The swivel shackle locks at 0° or 90° via a plastic washer swivel lock.
