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Glossary of Terms


6061-T6: an aluminum alloy that has excellent corrosion resistance to air and salt water. It is an easily welded, tough alloy that responds well to anodizing.
7075-T6: the strongest aluminum alloy with strength comparable to many steels. Harken uses 7075-T6 in its Grand-Prix cylinders which are built to handle extremely high loads at minimal weight. A vigorous maintenance schedule is required when using this alloy, because corrosion resistance is lower than 6061-T6. Available in hardcoat- or clear-anodized finishes.


A bail is an eye that may or may not have an opening. The opening makes a difference when you are trying to attach it to something without an opening, such as a loop lashing. Padeyes and eyestraps are common types of bails.


Bearing properties are functions of contact area, material type, bearing cages, and whether the bearing rolls or slides.
Ball bearings: very low friction; low/medium load capacity.
Roller bearings: low friction; high load capacity.
Sleeve bearings: medium/high friction; extremely high load capacity.
Stainless steel is stronger than Torlon® thermoplastic and Torlon is stronger than Delrin® acetal resin. Because stainless is heavier and usually higher maintenance, Torlon is used in most high-load applications.
Contact Area
More contact between the bearing and the race increases friction, but also increases load capacity. Balls are loaded on small points, cylindrical rollers are loaded along their length, and sleeve bearings are curved around the shaft so a large portion is in contact. Unlike balls and cylinders, sleeves are not prone to being flattened by extreme or static loads because they already conform to the curvature of the shaft.
Motion (Rolling, Caged Rolling, or Sliding)
Sliding bearings (known as sleeve, plain, full-contact, bushing, or journal bearings) are very high strength, but have nothing to reduce friction between contact areas. At most, they have a low-friction sleeve between the surfaces. Rollers and balls avoid almost all of this friction because they do not slide against the race, though they can come in contact with each other. Caged roller bearings are separated from each other to avoid this.


A becket is closed bail on a block that may or may not open. It usually serves as a deadend within a purchase.

Caged Bearings

Caged bearings are roller bearings held in a cage that keeps them separated from each other and parallel to reduce friction. Caged bearings are used in winches and Black Magic blocks.

Captive Bearings

Captive bearings are ball bearings that are contained so they won't spill during product maintenance. Black Magic blocks have ball bearings held captive by the lip of the sheave. CB traveler cars feature ball bearings held captive by a wire guide.


Carbo blocks and Carbo-Cam cleats for moderate loads are made of a high-strength engineering resin embedded with long glass fibers. They are 60% stronger and 30% lighter than stainless-reinforced Classic blocks. The Carbo name comes from an additive that gives the blocks their color and UV-resistance, but Carbo-Cam cleats also contain a plastic-carbon fiber matrix.

Carbon Black

Carbon black is a color additive used in black Delrin® ball bearings, block sheaves, and sideplates to protect against UV exposure.


The Classic block line for low to moderate loads is based on Harken's founding designs. They are typically stainless steel or Delrin® acetal resin with stainless reinforcement straps. Many but not all Classics have stronger and lighter counterparts in the Carbo block line.

Clear-Anodized (or Clearcoat-Anodized)

Clear aluminum anodizing is an electrochemical process that produces a corrosion-resistant finish. It also hardens the surface, making components less prone to scratches and dents. It is "clear" because the protective layer isn't thick enough to change the color of the component (though dye can be added). More rigorous anodization, such as hardcoat, can give components a black or colored hue.

Control Blocks

Usually refers to blocks on a traveler car that are responsible for moving the car along the track, but sometimes refers to the blocks on the end controls.

Delrin® Acetal Resin

Black (white in older blocks) material which excels in small boat and low- to moderate-load applications. Delrin® acetal resin is used for bearings, sheaves, and sideplates.

Dynamic Loads

Loads which require frequent adjustment. To minimize trimming loads, friction reduction usually takes priority over static load resistance in dynamic load applications.

End Controls

Hardware on either side of a traveler track that pulls the car to that side of the track.


Endstops are used at each end of the track in a traveler system to absorb shock loads and prevent the car from rolling off the end of the track.

Fiddle Block

A fiddle has two sheaves like a double block, except one is above the other instead of both sharing the same axis. Unlike a spriddle, the sheaves are different sizes and the smaller sheave has a lower load capacity.


While this can also refer to rudders and centerboards, here it refers to metal or plastic sheathes that slip over the forestay. These sheaths have one to two boltrope grooves, making sail changes faster and easier than on boats with hank-on headsails. Harken Carbo Racing Foils are made for this purpose, but jib reefing and furling units also contain headstay foils over which the headsail is rolled.

Hard Lube-Anodized

Hard Lube-anodized aluminum includes all the corrosion-resistant properties of hardcoat-anodized aluminum with the additional benefits of a PTFE coating for a smoother surface and reduced friction.


Hardcoat aluminum anodizing is an electrochemical process that produces a corrosion-resistant finish with hardness characteristics second only to diamonds. Harken's hardcoating process is twice as thick as black anodization to provide extra protection against scratches, dents, superficial deformation, and corrosion.

Heli-Coil® Threaded Inserts

Thread inserts that provide stronger threading for fastener holes, distribute fastener loads over a larger area, and isolate dissimilar metals.

High-Beam Track

High-beam track has a taller profile than low-beam track. Use high-beam track in carriage systems that span unsupported areas with the track.

Holding Power

The ability of a ratchet block to hold a static load. Expressed in a ratio of force on the loaded side of the rope to force on the side of the rope exiting the block, holding power is especially useful for relieving loads on hand-held ropes (when the block is not turning).

LOUP® Soft Attachment

LOUPs are Yale-brand loop lashings. They contain coiled UHMW braid and are covered with a sleeve to protect from wear. Colored tracers in the sleeve denote load rating and indicate UV exposure.


Generic term for soft attachments with two ends. Lashings are usually tied with several loops between the two attachment points then tied off at the end. Approved lashing configurations are included in applicable Harken product manuals. Custom configurations should be approved by Harken Technical Service or an experienced rigger.

Loop Lashing

Generic term for continuous circular soft attachments. While lashing configurations should be designed and tied by a professional, loops are strong and very simple to use because they don't require knots. Approved loop configurations are included in applicable Harken product manuals. Custom configurations should be approved by Harken technical service or an experienced rigger.

Maximum Working Load (MWL)

Never, under any circumstances, exceed the capacity or maximum working load (MWL) of any piece of equipment. The maximum working load may be found in our catalog, on our website, or through our technical service department. Loads above the MWL can cause the equipment to fail suddenly and unexpectedly.
Maximum working loads are a coefficient ratio of the breaking load. Human suspension applications require a 10:1 ratio.You must carefully read, understand, and follow all of the warnings and instructions in the User Manual provided by Harken in order to avoid an accident.

Nylatron® Nylon

Durable, lightweight composite material that has high mechanical strength and stiffness, resists static electricity, and has excellent wear resistance.


PTFE-coating, along with anodization, protects aluminum against corrosion by sealing the surface from moisture. It also minimizes friction and gives the component better wear resistance.

Pinstop Cars

Pinstop cars have a lever that is used to control the range of movement or lock cars in position along the track. Open the pinstop to move; close to lock in place.


A ratchet is a mechanism that holds part of the load on a block, letting you pull and release with complete control. Ratchets make it much easier to hand-hold higher loads by only allowing the sheave to turn in the trimming direction. This reduces muscle fatigue and offers better control when easing the sheet. Ratchets also make trimming easier since you don't have to hold the full force of the load while shifting your grip.

Roller Bearings

Roller bearings have greatly increased bearing contact surface area over ball bearings. This increases the strength and load capacity, but can also increase friction. For the best combination of high-strength and low-friction hardware, we use caged roller bearings.

Self-Tailing Jaws

A self-tailing winch allows the rope to be automatically and properly pulled and paid out. The "jaws" are a facing pair of clamping rings at the top of the winch drum with an angular shaped groove between them for the rope. The self-tailing jaws support a stripper arm for feeding the rope from the drum to the groove and paying out rope from the groove.

Set Screw

Several parts use set screws that can be tightened and loosed via hex wrench or screwdriver, making it easy for users to customize settings such as a Ratchamatic block's engagement tension, a pulley's shackle direction, or a hydraulic relief valve's threshold.


A U-shaped bracket, the open end of which is closed by a removable bolt (shackle pin), used for securing ropes, chains, etc.


A sheave (pronounced "shiv") is the wheel of a block with a groove along its edge for holding a line or cable.


Sideplates are the outer faces of a block that hold the sheave (wheel) in place. Sideplates can be made of lightweight composites, hardcoat-anodized aluminum, stainless steel, or titanium depending on the load requirements of the application.

Sleeve Bearings

Sleeve bearings (also known as full-contact, plain, bushing, friction bearings, or journal bearings), are cylindrical inserts that provide a low-friction layer for two surfaces to slide against each other, such as a pulley sheave turning on a journal. Sleeve bearings are excellent for very high loads as they distribute the load over a large surface. For lower loads, roller bearings or ball bearings are preferred because bearings that roll have significantly less friction than bearings that slide.

Soft Attachment

A term encompassing lashings, loop lashings, and any other fiber-based equipment that replaces the function of a shackle or padeye. They offer incredible weight savings over traditional shackles and padeyes made with stainless steel. However, they are prone to wear and should only be used on regularly maintained race boats.

Spriddle Block

A spriddle has two similarly sized sheaves like a double block, except one is above the other instead of both sharing the same axis. Unlike a fiddle, the sheaves have the same load capacity. Spriddles are often used for spinnaker changes and peels.

Stainless Steel

17-4 PH stainless steel: this alloy is used in gears because it is hardenable to extremely high strengths. 17-4 PH is more corrosion-resistant than any other standard hardenable stainless steel.
316 stainless steel: this is a nonhardenable alloy with high corrosion resistance in freshwater and saltwater.
XM-19 stainless steel: this stainless is highly alloyed, with very high mechanical strength and superior corrosion resistance. Rods and pins in Harken cylinders are made of XM-19 stainless.

Static Loads

Light to heavy loads that do not require frequent adjustment. Constant stress deforms certain materials, so strength takes priority over friction reduction in equipment designed for static loads.

Stripper Arm (Also Called Self-Tailing Arm)

The stripper arm peels the top wrap of rope off the winch drum as it is turning so it does not bunch up at the top. Winches without these require two-handed or two-person operation to manually strip the rope while turning it.


This lightweight, hard metal has the highest strength-to-weight ratio of any metal. Its corrosion rate is so low that after 4000 years in seawater, corrosion would only have penetrated to the thickness of a thin sheet of paper. Harken uses titanium rollers in V blocks to handle bearing loads.

Torlon® Thermoplastic

Exceptionally strong crush/impact-resistant bearing material that withstands heavy, long-term use and shock loading. Most Harken hardware that sees extreme loads uses greenish-brown Torlon® bearings.


UV light photo-degrades composites by breaking their chemical bonds, leaving them weak, brittle, and discolored. This is common in equipment with white bearings. All Harken composites and bearings are naturally UV-resistant or use stabilizers like carbon black.

Weather Helm

When heeled, the helm must be pulled windward ("to weather") to counteract the hull's tendency to turn windward. Ways to reduce weather helm for a faster and flatter ride include depowering the sail with the traveler and other controls.

Wire Block

Wire blocks are ideal for wires as well as lines used in high-load rigging applications. They have aluminum sheaves to stand up to the extreme loads and abrasive materials. Some wire blocks use stronger bearing materials and configurations.