Knockout Tools

LS100X Intelli-Punch |
Published On
Jan 14, 2022

In addition to basic hand tools, electricians also depend on single-purpose tools for specific applications. The knockout tool, or punch, is used to make clean, round, conduit-sized holes in metal electrical boxes and panels, as well as punching through aluminum and fiberglass.

The knockout tool has significantly changed the task of hole-making by creating clean holes faster than what is possible with other methods.

Rob Bentley, senior project manager at Greenlee, Rockford, Ill., said Greenlee patented and introduced the knockout tool in 1928.

“Prior to that, a common method for making a hole in sheet metal was to drill a small hole and then ream it out to the desired size,” Bentley said.

“A second method was for one person to hold a heavy piece of metal against one side of the box where the hole was to be made while another worker chiseled out the desired opening. Given that the desired hole size could be as much as 4½ inches, making holes of this size was very laborious and time consuming.”

Today’s knockout tools can punch holes in a variety of materials, he said. Interchangeable knockout punches are available for up to 10-gauge mild steel and 10-gauge stainless steel.

“Stainless-steel punches are built with a superior grade of tool steel to extend its punch life,” Bentley said. “Round knockout punches designed for mild steel also will punch stainless steel, but it should not be expected to last nearly as long as those designed specifically with stainless steel in mind. Either of these solutions is also capable of punching less common materials such as aluminum, plastic and fiberglass.”

Bentley said it is important to properly align the tool and that it does not shift position when the punch is made.

Bentley said components of a knockout tool are the punch, die, draw stud and element that applies to make the cut.

While these basic components have remained consistent over the years, knockout tools have evolved to offer users more efficient operation and better ergonomic design to handle the tool.

“For example, Greenlee has improved the knockout process by making enhancements to both the drivers and the knockout parts,” Bentley said.

The improvements include the following:

  • Battery-powered hydraulic drivers. Greenlee battery-powered hydraulic knockout drivers are compact and lightweight, with a swivel head that makes for minimal exertion during setup and use while still delivering the same capacity, durability and reliability of traditional Greenlee knockout tools. For example, the 7-ton LS50 and 11-ton LS100X Intelli-Punch tools have a fast cycle time with maximum trigger time of 8 seconds and will detect when a punch is complete. The LS100X Intelli-Punch tool goes one step further by automatically retracting the ram upon punch completion, which makes for faster disassembly.

  • Knockout parts. Many common Greenlee kits now come with taller, deeper dies that are deep enough to eliminate any chance of “overpunching” (continuing to drive a punch into the bottom of the die after the hole is complete). This puts less stress on all parts and saves the user the added cost of repairs and replacement parts.

  • Push-button knockouts for stainless steel. Designed for panel shops that install devices such as pushbuttons, switches, etc., these knockout sets save time by punching the hole (22.5 mm or 30.5 mm) and the required side notch in a single step. With an update to an existing product, the new KS-PB30 and KS-PB22 sets will punch up to 12-gauge stainless steel for panel shops that commonly work with this material. These sets are designed to work with any Greenlee hydraulic knockout driver.

What should tool buyers look for when evaluating knockout tools? Bentley suggests these points to consider:

  • Tool capacities. This includes the hole sizes, material types and material thicknesses the tool can punch. Select a tool that punches the largest size in the material and thickness needed.

  • Swivel head. A knockout driver that features a 360-degree rotating cylinder provides easier setup and a better working posture compared to a tool with a fixed head. This helps reduce an operator’s overall physical exertion.

  • Operational speed. Battery-powered hydraulic knockout drivers offer significant speed advantage over manual hydraulic tools. For example, Greenlee’s battery-powered hydraulic drivers feature a maximum “trigger time” of 8 seconds. A battery-powered tool will punch a hole in 10-gauge material twice as fast as a mechanical/hydraulic or mechanical tool.

  • Compact and lightweight design. Lightweight tools are easier to maneuver and require less physical exertion. Greenlee’s Intelli-Punch tool weighs 6.1 pounds with the battery, which is 40% less than the closest competing product.

“When preparing a cabinet for knockouts, the user begins by drawing crosshairs on the material surface long enough to extend the markings beyond the die radius,” Bentley said. “When setting up the knockout punch assembly, the user lines up the die’s alignment markings with the crosshairs, ensuring that the finished hole is accurately positioned. Once the user threads the punch onto the draw stud and tightens it down to material such as a cabinet, for example, the tool will remain fixed to the cabinet and knockout assembly until the hole is completed. On a Greenlee LS50 or LS100X tool, the swivel head allows positioning of the tool in the most comfortable orientation for the user.”

Greenlee offers a wide selection of knockout tool sizes for making 55 sizes of round holes, ranging from 0.492 inches to 6.75 inches, which will accommodate 6-inch conduit. The round punch selection covers the complete range of conduit sizes, metric trade sizes and several fractional sizes. Specialty “nonround” knockouts are also available in various shapes and sizes: rectangular/square, push-button (oil tight), “D,” “double-D” and other electronic connectors.

M18 Force Logic Knockout Tool | / Milwaukee Tool
M18 Force Logic Knockout Tool |
Milwaukee Tool

Troy Marks, group product manager at Brookfield, Wis.-based Milwaukee Tool, said there are many ways electricians can make holes, but the invention of the knockout tool offers a much more accurate and precise method. Each knockout tool has a set of punches and dies, a draw stud and a mechanism to pull the draw stud such as a hand wrench, hand hydraulic pump or mechanism.

Knockouts today are rated to punch mild steel, stainless steel or both.

“Milwaukee’s M18 Force Logic knockout tools are rated to punch both mild steel and stainless steel in diameters from ½ to 6 inches,” Marks said.

Improving the speed of the knockout tool process has been a focus in knockout tool evolution at Milwaukee, Marks said.

“We have built our system from the ground up, bringing a fresh perspective to the category of tools that has not only improved, but redefined the process that allows users to quickly align their punches and dies with vivid red crosshairs independently of the tool,” he said. “With our quick-connect system, a user no longer has to juggle the weight of the tool while trying to line up the punches and dies.”

Setting up the punch and die on the material is traditionally one of the most challenging steps in the hole-making process because alignment lines can be difficult to see and the weight of the tool that is attached to them works against users as they try to align them.

All dies have some sort of alignment mechanism, such as a small hash mark on the side.

“Milwaukee’s Exact punches and dies feature bold, red crosshairs that makes alignment fast and easy,” Marks said. “The tool is not the part that is kept in position. The user tightens the punch and die on the material, and then the pulling mechanism pulls straight up to make the punch.”

This can be a challenge because the weight of the tool can work against the user as they try to align.

“This is another area where Milwaukee has been very innovative,” Marks said. “Our punches and dies are set up separate from the tool for extreme ease of use. Utilizing a quick connect alignment system, the user can snap the tool onto the punch and die once set up is complete and pull the trigger to punch the hole with ease.”

Marks said knockout buyers should consider the tool’s capacity, capability, ease of use and system compatibility. He elaborated on each of these:

  • Capacity—A knockout tool buyer should choose a tool that can punch all the hole sizes they would need to make.

  • Capability—Some tools are rated for mild steel, stainless steel or both. Understanding the materials that will be frequently worked with will help determine which punches and dies will be needed.

  • Ease of use—Setting up the punches and dies can be difficult, but Milwaukee’s Exact punches and dies simplify the process with their bold, red crosshairs that help make alignment fast and easy.

  • System compatibility—Milwaukee’s knockouts use the M18 battery platform that can be used to power a wide range of M18 tools.

About the Author

Jeff Griffin

Construction Journalist

Jeff Griffin, a construction and tools writer from Oklahoma City, can be reached at

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