Lewmar 50mm Synchro Block Single Becket, 990 lb Working Load Limit, 1/4 - 3/8 Inch Line

The Lewmar 50mm Synchro Block Single Becket is a sailboat block built for efficient line handling on halyards, mainsheet systems, mast foot and head applications, and boom vangs. It uses a 50mm sheave with a 990 lb working load limit and accommodates line diameters from 1/4 inch to 3/8 inch, making it suited to a wide range of small to mid-size sailboat rigging setups.

The block's geometry and larger sheave diameter are engineered to minimize rope friction, while a high-density Free-Spin bearing reduces axle diameter to cut friction further and boost overall efficiency compared to standard budget blocks. A self-aligning head keeps the block synchronized with the rope's movement for smoother power transfer and reduced rope wear during use. The single becket design provides a fixed attachment point for tying off a line, useful in multi-part purchase systems.

Construction pairs stiff, glass fiber reinforced cheeks, which help prevent lines from wedging, with a stainless steel strap for added strength and long-term durability in a marine environment. The block allows an easy switch between swiveling and fixed shackle configurations, and its shackle post is designed for compatibility with Lewmar traveler systems. The complete unit includes one block with becket, ready to install on compatible sailboat hardware.

Specifications

• Brand: Lewmar
• Manufacturer Part Number: 29925004BK
• Product Name: 50mm Synchro Block Single Becket
• Sheave Diameter: 50mm
• Working Load Limit: 990 pounds
• Line Diameter Range: 1/4 inch - 3/8 inch
• Bearing Type: High-density Free-Spin bearing
• Becket: Single becket
• Shackle Configuration: Switchable between swiveling and fixed
• Cheek Material: Glass fiber reinforced
• Strap Material: Stainless steel
• Color: Multi
• Number of Items: 1
• Included Components: Block
• Package Dimensions: 5.75 x 2.56 x 1.38 inches
• Weight: 0.9 pounds
• UPC: 743683203756

Frequently Asked Questions

What line diameter fits the Lewmar 29925004BK Synchro Block? The Lewmar 50mm Synchro Block Single Becket (29925004BK) accommodates line diameters from 1/4 inch to 3/8 inch.

What is the working load limit of this Lewmar block? The 29925004BK Synchro Block has a working load limit of 990 pounds.

Does this block have a becket? Yes, the Lewmar 29925004BK is a single becket version, providing a fixed tie-off point for a line.

Can the shackle be switched between swiveling and fixed? Yes, the Lewmar Synchro Block 29925004BK allows an easy switch between swiveling and fixed shackle configurations.

What is the sheave diameter on the 29925004BK block? The sheave diameter is 50mm on this Lewmar Synchro Block.

What materials is the Lewmar Synchro Block made from? Glass fiber reinforced cheeks are paired with a stainless steel strap on the 29925004BK, combining stiffness at the cheeks with added strength from the steel strap.

Is this block compatible with Lewmar traveler systems? Yes, the 29925004BK shackle post is designed for compatibility with Lewmar traveler systems.

What sailing applications is this block suited for? Halyard tuning, mainsheet systems, mast foot and head blocks, and boom vangs are typical applications for the Lewmar 50mm Synchro Block Single Becket.

How does the Free-Spin bearing improve performance? The high-density Free-Spin bearing in the 29925004BK reduces axle diameter, which lowers friction and improves efficiency compared to standard budget blocks.

What is included when I order the 29925004BK? One Lewmar 50mm Synchro Block Single Becket is included, ready to mount to compatible sailboat hardware.

How much does the Lewmar 29925004BK block weigh? The Lewmar 29925004BK Synchro Block weighs 0.9 pounds.

Why do the block cheeks matter for line handling? The glass fiber reinforced cheeks on the 29925004BK are stiff enough to help prevent lines from wedging between the sheave and cheek during use.