Harken
Harken 421 16mm Thru-Deck Ball Bearing Block
The Harken 421 16mm Thru-Deck Block is a compact, flush-mounted ball bearing block designed to route control lines cleanly through decks, bulkheads, cockpit soles, and spars. Part of Harken's renowned 16mm Micro Block range, the 421 provides a tidy, low-profile solution for internal line routing while maintaining the smooth, low-friction performance Harken is known for.
Featuring a 16mm Delrin® sheave running on Harken's patented stainless steel captive ball bearing system, the 421 delivers effortless trimming and excellent durability in demanding marine environments. Its flush installation reduces deck clutter, protects control lines from snagging, and provides a professional finish for both new builds and yacht upgrades.
Designed for synthetic control lines up to 5mm diameter, the Harken 421 is ideal for internal outhauls, cunninghams, reefing lines, traveller controls, halyard exits, and other concealed sail-control systems on dinghies, skiffs, sports boats, trailer yachts, and performance cruising yachts.
Key Features
- Genuine Harken Part No. 421
- Flush thru-deck block for concealed line routing
- 16mm Delrin® sheave
- Patented stainless steel ball bearing system
- Captive grooved bearing race
- Low-profile installation
- Handles rope up to 5mm diameter
- Lightweight yet exceptionally strong
- Corrosion-resistant marine construction
- Suitable for decks, bulkheads and spars
- Smooth, low-friction operation
- Genuine Harken quality
Why Buy from Barton Marine NZ?
At Barton Marine NZ, we stock genuine Harken sailing hardware trusted by sailors throughout New Zealand. The Harken 421 is the ideal solution when you want clean internal rigging, reliable performance, and minimal deck clutter.
Perfect for:
- Racing dinghies
- Skiffs
- Catamarans
- Sports boats
- Trailer yachts
- Performance cruising yachts
- Internal control-line systems
- Mast exits
- Boom exits
- Custom yacht builds
Technical Specifications
| Feature | Specification |
|---|---|
| Brand | Harken |
| Part Number | 421 |
| Product Type | Thru-Deck Ball Bearing Block |
| Sheave Diameter | 16mm |
| Sheave Material | Delrin® |
| Maximum Rope Diameter | 5mm |
| Overall Length | 60mm |
| Weight | 18g |
| Mounting Fasteners | 4mm (#8 RH) |
| Deck Cut-Out | 11 × 35mm |
| Maximum Working Load | 113kg |
| Breaking Load | 544kg |
| Bearing System | Stainless Steel Ball Bearings |
| Marine Suitable | Yes |
These specifications are published by Harken for the 421 16mm Thru-Deck Block.
Common Applications
The Harken 421 is ideal for:
- Internal outhaul systems
- Cunningham controls
- Reefing line exits
- Halyard exits
- Traveller control lines
- Internal boom controls
- Mast line exits
- Bulkhead line routing
- Deck-mounted control systems
- Lightweight performance rigging
Performance Benefits
The Harken 421 delivers:
- Clean, flush deck installation
- Smooth, low-friction line movement
- Reduced deck clutter
- Protection against line snagging
- Lightweight construction
- Reliable stainless steel ball-bearing performance
- Excellent durability in harsh marine conditions
- Professional finish for modern yacht rigging
Its compact thru-deck design allows control lines to pass neatly through the deck or spar while maintaining efficient line handling and minimising friction, making it a popular choice for modern racing and cruising yachts.
