Lewis Pins and Lifting Holes for Dimension Stone Blocks

A block of dimension stone has no handles. It has no flanges for a hook, no eyes for a shackle, and a surface that the people paying for it do not want scarred by chains. For a very long time the answer to that problem has been the lewis: a steel fitting set into a hole cut into the top of the block, which grips the stone from inside and gives the crane hook something to pull on. Lewises are still found in monument shops, restoration work and architectural stone yards, and lewis pins are sold today as current stock for lifting granite.

This guide covers the main lewis types, how their holes are prepared and positioned, which blocks are good or poor candidates for one, how to inspect the gear and the stone, and where clamps, vacuum lifters and slings now do the job better. It also sets out the rigging rules from OSHA and the ASME B30 standards that apply to any below-the-hook lift. It does not give load ratings for any lewis or block, because those must come from the manufacturer of the specific device and from a competent person assessing the specific stone.

How a Lewis Grips Stone From the Inside

Every lewis works on the same idea. A hole is made in the top bed of the stone, a set of steel pieces is placed in it, and when the crane takes up the load the pieces are forced outward or locked against the walls of the hole. Some types rely on friction: the weight of the stone loads long lever arms, which press short arms hard against the sides of the hole. Others rely on shape: the hole is undercut so it is wider at the bottom than at the top, and the assembled lewis cannot pull out through the narrower mouth.

Lewises have a long history. Roman builders used them, and a geological society study of how historic stone was moved describes the three-legged lewis as a Greek invention used extensively by the Romans, with lewis holes still visible in surviving blocks. In finished masonry the holes were usually on the top bed, where the next course would hide them, and where a hole was left exposed it was typically repaired with a matching stone plug. An old lewis hole is not proof that a block is safe to lift by it today.

The three-legged or dovetail lewis

The three-legged lewis is the classic form. It consists of three steel pieces that together form a dovetail: two outer legs, each tapered, and a straight centre leg or spacer. The hole is cut to match the profile, undercut so that it is wider at the bottom. The two outer legs go in first and are pushed against the sloping walls, then the centre piece is inserted between them, locking them apart. A pin passes through the tops of all three pieces and through a shackle or ring that takes the crane hook. Because it grips by shape rather than friction alone, masonry references describe it as the most secure type, though the hole takes the most time to prepare.

Lewis pins and two-pin lewises

Lewis pins are the type most fabricators will meet today. They are steel pins sold in pairs, each set into its own drilled hole, with the two holes angled toward each other so that the pins pinch the stone between them when the sling or chain linking them is pulled tight. Current suppliers sell them specifically for lifting granite and specify the drill bit diameter that matches each pin size. The hole is quick to make with a drill rather than a chisel, but masonry references note that pin lewises can pull out during a lift, so the drilling angle, depth and hole fit given by the pin maker matter.

Split-pin and chain lewises

A split-pin lewis uses two half-round legs placed side by side in a single drilled hole. When load is applied the legs act like a pair of scissors and bear against the inside of the hole, so the preparation is the simplest of any type. The chain lewis uses curved steel legs linked by rings, seated in a cut that is undercut to match their profile; pulling the rings together forces the lower ends outward. The term lewis bolt has also been used historically for a wedge-shaped bolt fixed in its socket with lead, which is a permanent fixing rather than a reusable lifting tool.

Drilling, Positioning and Rigging a Lewis Lift

Preparing a lewis lift is mostly about the hole and its location. The device itself is simple; the stone around the hole and the balance of the block decide whether the lift is controlled. The table below compares the common lifting methods for blocks and slabs in qualitative terms, as a starting point for deciding which method fits a given piece. Specific capacities and limits always come from the manufacturer's instructions and marking for the device in hand, never from a general guide.

Locating the hole over the centre of gravity

A single lewis should sit directly above the block's centre of gravity. Rigging guidance from university safety offices and training bodies says the same thing for any lift: the hook must be directly over the centre of gravity to make a level lift, and if it sits to one side the load tilts and stresses the rigging unevenly. For a regular rectangular block of uniform stone the centre of gravity is at the geometric centre, so the hole goes in the middle of the top bed. For irregular, tapered or partly worked blocks, estimate the centre of gravity carefully before choosing the hole position.

Long or heavy blocks are often lifted with more than one lewis. Historic practice used two or three lewises to keep a block balanced during the lift, and modern rigging guidance makes the same point about spreading load across more attachment points. With two lewises, place them symmetrically about the centre of gravity and use a spreader beam or a bridle of equal-length legs so the hook stays central. Remember that the angle of each leg affects the tension in it: as the angle between the sling leg and the horizontal decreases, the load in that leg rises and its usable capacity falls.

Drilling and cutting the seating

For lewis pins, drill with a bit of the diameter the pin maker specifies, at the angle and depth their instructions give, and keep both holes in the same plane so the pins bear symmetrically. A diamond core bit or a suitable rotary bit on a drill held steady by a guide gives a cleaner, more accurate hole than freehand drilling. Clear all dust and slurry from the hole; debris trapped under a pin changes how it seats. For a dovetail lewis the seating is traditionally cut with chisels and checked against the actual legs that will go into it, so that all three pieces seat firmly without being forced.

Stone condition and block limits

The stone around the hole has to carry the entire weight of the block, so its condition decides whether a lewis is appropriate at all. Avoid placing a hole near a visible crack, vein, vug, open bedding plane or previous repair, and be cautious with stone that is weathered, friable or soft. A study of historic stone lifting notes that granite can be less suitable because it can be brittle, and that many old lewis holes show broken rock around the top. When a block is badly fractured, very irregular, or of unknown weight, a lewis is the wrong tool and the lift should be planned by a qualified rigger.

Regulations, Inspection and Modern Alternatives

In the United States, OSHA's construction rule for rigging equipment for material handling, 29 CFR 1926.251, sets the baseline. Rigging equipment must be inspected before use on each shift and as necessary during use, and defective gear must be removed from service. Rigging must carry permanent markings showing the manufacturer's recommended safe working load and must not be loaded beyond it. Special custom-designed grabs, hooks and clamps must be marked with their safe working load and proof-tested before use to 125 percent of their rated load. A shop-made lewis falls squarely into that category.

The ASME B30 family of consensus standards adds detail. ASME B30.20 covers below-the-hook lifting devices, with chapters for structural and mechanical lifting devices, vacuum lifting devices, lifting magnets, grapples and clamps, and it sets requirements for marking, inspection, testing, maintenance and operation. ASME B30.9 covers slings, and ASME B30.26 covers rigging hardware such as shackles, eyebolts and swivel hoist rings. OSHA rules are law; ASME standards are often referenced by manufacturers, insurers and inspectors, so stone shops benefit from following both.

Inspecting the lewis and the hole

Before each use, check every lewis piece for cracks, bends, wear at the bearing faces and deformation of the pin holes, and check the shackle and pin for wear and correct fit. Any lewis that has been ground, heated, welded or repaired should be withdrawn until a competent person has approved it. Inspect the hole as well: look for spalling at the mouth, hairline cracks radiating outward, enlargement from previous use and debris inside. Masonry practice is to correct looseness by adjusting the hole or packing with metal shims, and to replace rather than improvise when the fit cannot be made sound.

Then make a test lift. Raise the block only a couple of inches, stop, and check that it hangs level and that nothing has moved in the hole. Rigging guidance from university safety programmes gives the same instruction for any load: lift it slightly first, check the balance, and adjust before going further. Keep everyone out from under the suspended block and out of the path it will travel, use a tag line to control rotation where the layout allows, and set the block down on dunnage so the lewis and any sling can be removed without trapping fingers.

Clamps, vacuum lifters and slings

For most fabrication and installation work, lifting devices that need no hole have largely taken over. Mechanical stone clamps close their jaws on opposite faces of a block or slab, and the weight of the load increases the grip; they need parallel faces within the clamp's stated jaw range and pads in good condition. Vacuum lifters hold a flat face by suction and leave no mark, but surface porosity, texture and pad condition all affect the seal, so follow the maker's guidance on which materials and finishes the unit is rated for and on its warning devices and reserve capacity.

Slings remain the simplest option for rough blocks. Choose synthetic web or round slings for finished stone to avoid marking, protect every sling from sharp arrises with corner pads or sleeves, and remember that OSHA requires slings not to be shortened with knots, bolts or other makeshift devices. Check the sling's tag for its rated capacity in the hitch you plan to use, and account for the reduction that comes with lower sling angles. A basket hitch under a block that may roll, or a choker on a slab with sharp edges, can fail even when the weight is well within the tag rating.

Keeping Lifting Gear and Records in Good Order

Long-term safety with stone lifting depends on discipline as much as equipment. Give every lewis, clamp, vacuum lifter and sling an identifier, keep its marking legible, and log inspections and any repairs. ASME B30.20 distinguishes between frequent inspections and complete periodic inspections, with intervals set by service severity, and requires a qualified person to approve the return to service of any device removed for a hazardous condition. Even a small shop can run a simple logbook that records who checked what, when, and what they found.

Store lifting gear dry and off the floor, away from grinding swarf and acid cleaners that can corrode steel or degrade synthetic slings. Keep lewis sets together as matched sets, because a dovetail lewis is only secure when its legs match each other and the seating cut for them. Retire pins and legs that show visible wear rather than mixing them into other sets. For vacuum lifters, follow the maker's schedule for pad replacement, filter changes and checking the gauge and alarm, and test the unit on a known load as the manual directs.

For hole-free handling of blocks and slabs, browse our slab lifters and clamps, including the Aardwolf Horizontal Stone Lifting Clamp, and the range of vacuum lifters. For sling-based lifts there is the Aardwolf Endless Webbing Sling, and for accurate pin holes our core bits cover a wide range of diameters.