Seldén single blocks for dinghy and keelboat control lines, mainsheets, spinnaker sheets and halyards, spanning the BBB, PBB and S-series soft attachment ranges from 16 mm to 60 mm sheave diameter with plain bearing, ball bearing and ratchet options.
How to choose
Start with sheave size and line diameter. Smaller sheaves suit lighter loads and thinner lines; larger sheaves reduce friction on heavier lines and higher loads. As a guide: the 16–20 mm range suits lines up to 6 mm on light applications such as flag lines, lazy jacks and trim lines on smaller dinghies. The 25–30 mm range covers lines up to 8 mm on single-handed dinghy control lines and mainsheets. The 40–60 mm range handles lines up to 10 mm for mainsheets, spinnaker sheets and higher-load systems on two-handed dinghies and keelboats.
Next, choose bearing type. Plain bearing (PBB) blocks are suited to heavy, slow-moving or static loads such as halyard tuning, vang systems and boom vangs where the line moves infrequently. Ball bearing (BBB) blocks are the right choice for dynamic loads where the line runs frequently and friction must be minimized. For mainsheets and spinnaker sheets where load is high and you want to hold the line without cleating, a ratchet block is the practical choice.
Then choose the attachment type that fits your fitting point and application. Swivel blocks work where the lead angle changes. Strap and fixed-pin blocks suit fixed attachment points. Tie-on blocks give a lightweight, articulating fit on a boom, mast base or other lashing point. Cheek blocks mount flush to the deck for turning lines. Soft attachment blocks mount with a Dyneema lashing or soft shackle and are particularly popular on boats where snagging points need to be minimised.
Becket variants add a secondary attachment point to the block body, useful for anchoring the standing end of a purchase system. Cam cleat variants integrate a line-holding cleat directly into the block, reducing the need for a separate cleat fitting.
For ratchet blocks, decide between manual and automatic. Manual ratchet (R60) requires the sailor to switch the ratchet on and off. Automatic ratchet (ARB45, A60) engages as load increases, with the switchover point adjustable with an allen key — useful when load varies and hands-free engagement is preferred.
What's in this collection
The PBB16 plain bearing blocks are 16 mm blocks suited to flag lines and lazy jacks on lines up to 6 mm, available in composite (401-001-01) and brass (401-001-02) versions.
The PBB20 plain bearing blocks are 20 mm blocks for flag lines, lazy jacks and light trim lines up to 6 mm. The standard single (402-001-01) suits fixed routing applications. The Flip-Flop variant (402-001-02) is designed for dinghy trim lines including cunningham, outhaul and halyard.
The BBB20 ball bearing blocks are 20 mm blocks for control lines up to 6 mm on dinghies and keelboats. Attachment options include strap (402-101-01R), becket (402-101-02R), shackle (402-101-09R), tie-on (402-101-12R), cheek (402-101-13R), lead (402-101-16R) and through-deck lead (402-101-17). The Optimist Sprit Block (402-101-22) is a BBB20 variant with an integrated hook designed to engage in the front of a Seldén Optimist mast, with a base radius matched to the mast tube. Soft attachment singles are available in the standard S20 Acetal sheave version (402-101-60R, with 2 mm / 550 mm lashing included as a separate variant 402-101-62R), an upgraded S20+ with stainless sheave (402-101-65R), and a complete kit (402-101-60-01R).
The BBB25 high load ball bearing blocks are 25 mm blocks rated for lines and wire up to 5 mm, built for dynamic loads on smaller boats with halyards, control lines and tackles. Attachment options are strap loop (402-201-04R), fixed pin (402-201-05R), removable pin (402-201-06R) and becket with removable pin (402-201-07R).
The BBB30 ball bearing blocks are 30 mm blocks for lines up to 8 mm. Attachment options include swivel (403-101-01R), strap (403-101-02R), swivel becket (403-101-03R), tie-on (403-101-08R), cheek (403-101-09R), stand-up eyestrap (403-101-12R), becket strap (403-101-13R) and clew/stainless ring (403-101-14R, suited to 2:1 jib sheets on keelboats). Soft attachment singles are available as the S30 with Acetal sheave (403-101-60R) and the S30+ with stainless sheave (403-101-65R).
The PBB40 plain bearing blocks are 40 mm blocks suited to heavy or static loads up to 8 mm including halyard tuning, mainsheet systems and boom vangs. Available as swivel (404-001-01R), swivel becket (404-001-02R) and strap (404-001-25R).
The BBB40 ball bearing blocks are 40 mm blocks for dynamic loads up to 10 mm. Attachment options include swivel (404-101-01R), strap (404-101-02R), swivel becket (404-101-03R), swivel cam (404-101-04R, integrated 27 mm composite cam cleat), swivel becket cam (404-101-05R), tie-on (404-101-16R), cheek (404-101-17R) and becket strap (404-101-20R). Soft attachment singles are the S40 with Acetal sheave (404-101-60R) and the S40+ with stainless sheave (404-101-65R).
The ARB45 automatic ratchet blocks are 45 mm blocks with automatic ratchet engagement, Delrin ball bearings and an aluminium sheave for grip on thinner lines. Available as a swivel/fixed shackle variant in two SKUs (404-360-51 and 404-401-01R), both suited to dinghy mainsheets and spinnaker/gennaker sheets.
The BBB60 ball bearing blocks are 60 mm blocks for lines up to 10 mm, suited to mainsheets, genoa and spinnaker sheets on larger dinghies and keelboats. Standard versions include swivel (406-601-01R), swivel becket (406-601-02R), swivel cam (406-601-03R, 38 mm composite cam cleat), swivel becket cam (406-601-04R) and tie-on (406-601-14R). Heavy duty versions with stainless ball bearing races handle higher loads: swivel (406-601-51R), swivel becket (406-601-52R) and tie-on (406-601-64R).
The R60 manual ratchet blocks feature a ø60 mm composite sheave with a manual switch on each side to select ratchet or free-spinning mode. Variants include swivel (406-350-01R), swivel becket (406-350-02R), swivel becket cam (406-350-04R, size 38 cam cleat with top guide), cheek clockwise (406-350-05R, starboard spinnaker sheet), cheek anti-clockwise (406-350-06R, port spinnaker sheet) and the R60+ with aluminium sheave for added grip on finer lines (406-360-01R), available in two SKUs.
The A60 automatic ratchet blocks feature a ø60 mm composite sheave with automatic ratchet engagement adjustable by allen key. Variants include swivel/fixed (406-350-51R), soft attachment composite sheave (406-350-54R), cheek clockwise for starboard spinnaker sheet (406-350-55R), cheek anti-clockwise for port spinnaker sheet (406-350-56R). The A60+ with aluminium sheave offers more grip on thinner lines: swivel/fixed (406-360-51R) and soft attachment (406-360-54R), available across two SKU sets.
The System 22 Jib Car (442-150-01) is a composite pinstop car for keelboats and larger dinghies, fitted with a BBB40 tie-on block on a Dyneema lashing. The forward dead-end provides a 2:1 purchase on the jib sheet, giving fast trim adjustment without reliance on a winch.
Dinghy class applications
The Optimist is the most specifically referenced class in this collection. The BBB20 Sprit Block (402-101-22) is purpose-built for the Optimist sprit halyard and fits all Seldén Optimist sprit sections. Smaller BBB20 and S20 blocks are also well suited to other Optimist control line applications.
Across other dinghy classes, block selection is application-driven rather than class-specific. BBB20 and S20 blocks cover trim lines on smaller single-handed boats. BBB30 and S30 blocks suit mainsheet and control line applications on mid-sized single-handed dinghies. BBB40, S40, ARB45 and the R60/A60 ratchet range cover mainsheet and spinnaker systems on two-handed dinghies and skiffs. BBB60 heavy duty blocks are most relevant to larger dinghies and small keelboats where loads are sustained and higher.
