• Sizing ranges from 22″ to 40″
  • Construction of single conductor type transmission lines, industry standard
  • Large enough for bigger conductors yet still light and easy to handle
  • Throat sections is sufficiently large to permit passage of sleeves and connections of most types encountered in new construction and reconductoring
  • Safety locking headpin
  • Available with urethane lining
  • Available block ground option



About Transmission Construction
Transmission-class line construction is very specialized. Structures are taller, spans are longer, conductors are larger/heavier/stiffer, and pulls are longer and can extend over steep and very uneven terrain. In addition, aluminum conductors vary in construction requirements, calling for special handling techniques, tools, and equipment.

Transmission construction also involves different line and structure designs, as well as different conductor configurations. Some lines are strung using conventional, ground-based equipment and tools, while others require stringing using helicopters.

The configuration and quality of the blocks in which sheaves are mounted are as important as the sheaves.

About 78 Series Transmission Blocks
The 78 Series single-conductor stringing blocks are an ideal choice for stringing large-diameter transmission-class conductor. These blocks are available with 20″, 22″, 28″, 35”, and 42″ (OD) sheaves, and they are light-weight, yet exceptionally rugged, reliable, and durable. Their low-friction bearings render high block efficiency, which helps to maximize stringing distances while minimizing pulling tensions and reducing loads on stringing equipment. Combined with the associated family of hardware and accessories, the 78 Series affords utilities and their contractors exceptional versatility in how and where it may be deployed and in the range of installation problems it can help solve.

The 78 Series blocks’ light weight and durability derive from the materials and methods used to make them. The material used for the frame is “virgin” A356-T6 Aluminum, which is an aluminum alloy with very tightly controlled proportions of other materials to assure optimum performance during manufacture and in the field. Virgin material is material that has not been mixed with scrap material, not even with scrap of what may have once been the same alloy. That Sherman & Reilly uses “virgin” material assures that the material is exactly and only the pure and correct alloy, and that it has not been contaminated by impurities (notably iron) that often accompany non-virgin material.

78 Series frames are cast (molded) as molten metal. The properties and purity of the A356-T6 Aluminum used by Sherman & Reilly assure that the molten metal flows smoothly and evenly throughout the mold, assuring proper and uniform density throughout the finished frame. Proper density and uniformity combined with the purity and metallic properties of the alloy assure that the frame is strong but light-weight, and assure that there are no internal voids or brittleness that could cause sudden complete failure of the block in the field.

The sheaves of the 78 Series are also made of the same virgin A356-T6 Aluminum as the frame. They are also similarly cast, but they have the additional manufacturing step of having the grooves and bearing surfaces machined for smoothness and precision fit. Combined with low-friction, lubricated-for-life bearings, the sheave materials and how they are made assure high-efficiency and smooth-stringing performance.

Configuring 78 Series Transmission Blocks
Configuring 78 Series transmission blocks is relatively easy to do, and it can be done using the information and tools on this website. Configuration requires that you determine:

1. Sheave size.
2. Sheave lining, if any.
3. Fitting (for hanging the block)
4. Attachments.

Sheave size is largely a function of the size of the conductor being strung and of span length and terrain over which the conductor will be installed. Sheave lining is largely a function of the type of conductor being used and/or requirements from the conductor manufacturer. Determining the fitting is simply choosing the hardware that slips into the socket connector at the top of the block. Attachments are a function of how the conductor will be installed and grounded.

Ordering 78 Series Transmission Blocks
Prepared with the above configuration information (or if you need any help configuring and/or ordering your blocks), you may order your blocks by consulting your Sherman + Reilly Representative or you may consult Sherman + Reilly directly. For help with configuring and pricing your from Sherman + Reilly directly, you may call 1-800-251-7780 ask for “Quotes.”

Complete Dimensions



Sheave OD in. Rim Width in. Groove Bottom Dia. in. CONNECTION POINT TO GROOVE BOTTOM in. throat
dimensions in.
Height OVERALL in. width overall in. groove radius in.


Urethane Polished


Urethane Height Width
Polished Groove Urethane
A B c D E F G H I
20 20 3 1/8 16 16 1/4 10 3/8 10 1/4 5 11/16 5 9/16 3 1/8 30 1/8 7 5/8 13/16
22 22 3 1/8 18 18 1/8 10 3/8 10 5/16 5 11/16 5 5/8 3 1/8 32 7 7/8 13/16
28 28 3 1/4 23 3/4 24 10 1/4 10 3/8 5 13/16 5 11/16 3 1/4 38 1/8 7 3/4 7/8
28-A 28 3 1/4 24 10 3/8 5 11/16 3 1/4 38 1/8 7 3/4 1
35 35 4 30 1/4 12 13/4 8 1/32 4 1/2 47 10 3/8 1 1/8
42 42 4 1/2 36 17 3/8 9 3/4 5 58 12 1/2 1 1/8
46.25 46.25 5.00 40.00 14.50 6.75 4.00 61.00 10.00 1.375


Size (NOM) maximum conductor od maximum working load lbs. block weight (NOM) LBS. Material Efficiency
frame sheave
20 Refer to IEEE Standard 524 (2016) 12,000 42 A356-T6 Aluminum- (virgin) 98%
22 12,000 46
28 12,000 62
28-A 12,000 68
35 12,000 115
42 17,000 155
46.25 20,000 185

Please refer to the Product Sheet found on this page under Downloads.