ToolsArmenia Knowledge Base

How to Choose the Correct Size of a Tool Accessory

The size of a disc, drill bit, masonry bit, core bit or chisel must match not only the job but also the tool’s permitted limits, attachment system, material and operating speed. This guide explains how to select accessory diameter, length and type without overloading the tool or reducing safety.

Reading time: about 17 minutesUpdated: July 2026ToolsArmenia Editorial Team

Which accessory dimensions actually matter?

A label such as “125 mm disc” or “10 mm masonry bit” does not describe full compatibility. In addition to diameter, check the bore or shank, thickness, working and overall length, maximum permitted speed and the applications approved by the tool manufacturer.

Working diameter

Determines the nominal size of the hole, cut or working area, but not always the actual maximum depth.

Working length

Shows which part of the accessory is designed to operate in the material. It differs from overall length.

Attachment size

The shank, bore, thread or attachment system must precisely match the tool’s chuck or spindle.

Permitted speed

The speed limit of a disc or other rotating accessory must not be lower than the tool’s actual operating speed.

Four required matchesSelect an accessory only when tool type, attachment system, permitted size and material application all match at the same time.

How to choose disc diameter

Disc diameter must be selected according to the size permitted by the tool manufacturer, not solely according to the desired cutting depth. A larger disc increases peripheral speed, load and required guarding space. It may not fit beneath the guard, may exceed the tool’s structural capability or may require a different speed class.

Parameter to check	What must match	Risk prevented
Outside diameter	The permitted size stated on the rating plate or in the tool manual.	Guard incompatibility, excessive load and unsafe speed.
Bore	The exact size and design of the spindle, flange or X-LOCK system.	Incorrect seating, vibration and disc damage.
Thickness and type	Cutting, grinding, diamond or other purpose according to the tool and material.	Incorrect side loading, overheating and ineffective work.
Maximum rpm	The accessory’s permitted speed must be equal to or higher than the tool speed.	Overspeed and disc failure.
Safety guard	The guard type, position and permitted diameter.	Uncontrolled direction of fragments and sparks.

What do common diameters mean?

The 100–125 mm class is generally selected for portability, control and small or medium jobs, using a tool designed for the size.
The 150 mm class is an intermediate solution that requires a tool and guard specifically intended for that size.
The 180–230 mm class is intended for deeper or heavier work and generally requires a larger tool, two-handed control and sufficient working space.

Never increase disc size yourselfDo not remove the safety guard or install a disc larger than the manufacturer permits on a smaller tool. A bore adapter does not change the tool’s permitted outside diameter or speed.

How to choose drill-bit or masonry-bit diameter

The nominal diameter of a drill bit or masonry bit usually determines hole size, but the final requirement must be linked to the fastening system or working method. For a plug, anchor or other fixing, follow the hole diameter and depth specified by the manufacturer of that exact fixing.

For wood

Select a design and diameter intended for wood. For a large hole or work close to an edge, consider the risk of splitting and the need for support.

For metal

As diameter increases, lower speed, stable clamping and suitable cooling or lubrication are generally required according to the material.

For brick and concrete

The SDS system, diameter and working length must match the rotary hammer’s permitted range and the fixing requirements.

For a through-hole

The working length must exceed the material thickness sufficiently for the flute to remove dust or chips.

Dimension	What it means	Selection error
Diameter	The nominal hole size in the correct material and operating mode.	Choosing by eye without checking the fixing requirement.
Working length	The usable section that works within the material.	Treating it as equal to overall length or required depth without clearance for dust removal.
Overall length	The complete measurement from the shank to the tip.	Ignoring the section inside the chuck and clearance from the tool body.
Shank	Cylindrical, hexagonal, SDS Plus, SDS Max or another attachment.	Using an incompatible or unapproved adapter.

Efficient diameter rangeThe stated maximum diameter is a limiting capability and not always the fastest everyday working size. For repeated work, also check the manufacturer’s recommended or optimum range when it is provided.

How to choose core-bit diameter

A core bit removes material around an annular path, but a large diameter requires substantial torque, correct speed and stable control. Begin with the required finished hole, then verify the material, the machine’s diameter range, attachment interface, pilot bit and whether handheld or rig-mounted use is permitted.

Finished hole — select nominal diameter according to the installation requirement, considering the actual outside size of the pipe, box or passing component and the necessary clearance.
Material — core bits for wood, metal, brick, concrete and reinforced concrete differ in design and operating mode.
Tool range — the exact machine must permit the diameter, material and handheld or rig-mounted method.
Attachment — check the thread, adapter, quick-release system and pilot-bit compatibility.
Depth — core-bit working depth must be sufficient and the core must be removable safely.
Cooling and dust control — use the wet or dry mode specified by the manufacturer and the appropriate water or dust-management method.

Large diameters require a dedicated setupDo not assume that a powerful drill or rotary hammer can operate any core bit. A large diameter may require low speed, a safety clutch, an auxiliary handle or a drilling rig.

How to choose chisel type and size

The type of demolition accessory determines how impact energy is transferred to the material. A narrow point concentrates force on a small area, while a wide blade distributes it across a larger surface. An excessively wide blade can reduce penetration, while an unnecessarily long accessory can increase bending load and reduce control.

Type	Main application	Size-selection logic
Pointed chisel	Local breaking of concrete or masonry and starting a fracture.	The point concentrates the impact; length is selected for access and tool class.
Flat chisel	General demolition, layer removal and edge work.	A narrower blade improves local penetration; a wider one increases surface coverage.
Tile chisel	Layer-by-layer removal of tile or covering.	Width and angle are selected for controlled movement beneath the covering.
Wide spade chisel	Removing plaster, mortar or softer layers over a large area.	A wide design covers the surface faster but is less effective for deep breaking of hard material.
Channel chisel	Forming a channel or groove in a suitable material.	Profile width and depth must match the required channel and tool capability.

Attachment system comes firstSDS Plus, SDS Max and HEX chisels are not directly interchangeable. Select the system and size explicitly permitted for the particular rotary or demolition hammer.

How to check the attachment system and full compatibility

Even when working size is correct, the wrong shank, bore or flange can make installation impossible or unsafe. Check compatibility using the exact markings on the tool and accessory rather than visual similarity.

Compare the chuck, spindle, thread or quick-change system specified in the tool manual with the accessory data.
Confirm that the chuck’s clamping range includes the shank diameter and shape.
For a disc, verify outside diameter, bore, flange, thickness and guard type.
For SDS or HEX accessories, select the same named system and a class permitted for the tool.
For a core bit, also check the adapter, pilot bit, extension and the complete attachment chain.

Do not modify the accessoryDo not enlarge a disc bore, grind down a shank or use a homemade adapter. Such changes compromise concentricity, strength and the manufacturer’s safety conditions.

How to relate accessory size to material and speed

Accessory size changes the required speed and tool load. At the same rpm, the edge of a larger rotating accessory has a higher linear speed, while the contact area with the material often increases. Speed setting, torque, cooling and feed must therefore meet the accessory manufacturer’s requirements.

Do not use the high speed intended for a small accessory with a large drill bit or core bit.
The maximum rpm marked on a disc is a limit, not a mandatory operating speed.
When drilling metal, match diameter and material to the correct speed and required cooling.
Relate concrete masonry-bit size to the rotary hammer’s recommended range, impact energy and dust-removal capability.
Relate chisel width to material hardness and the required penetration or surface removal.
If the tool loses speed, overheats or vibrates strongly, stop work and check the size, accessory and operating mode.

7 steps for selecting tool-accessory size

Define the finished result

Record the required hole, cut, groove or removed-layer size.

Confirm the material

Select an accessory specifically intended for wood, metal, brick, concrete, stone, tile or the relevant material.

Check the tool limits

Find the permitted diameter, length, attachment system and operating mode.

Select working length

Allow for material thickness, the section held in the chuck and clearance for chip or dust removal.

Confirm the attachment

Match the shank, bore, thread, flange or adapter to the tool.

Check speed and load

The accessory’s permitted speed and operating mode must suit the tool.

Carry out a controlled test

Begin in a stable position while monitoring vibration, sound, temperature and quality of work.

Frequently asked questions

Can an angle grinder use a disc larger than permitted?

No. A larger disc may not match the guard, speed, spindle or structural load of the tool. Use only the diameter permitted by the manufacturer and do not remove the safety guard.

Is an identical disc bore enough to confirm compatibility?

No. Outside diameter, thickness, disc type, maximum rpm, flange and safety guard must also match.

Does drill-bit diameter always equal the resulting hole?

It is the nominal hole size, but the actual result is affected by material, accessory wear, tool runout and operating mode. For a fixing, follow the requirement stated by its manufacturer.

Why is masonry-bit working length important?

It must provide the required hole depth and allow the flute to remove dust. Overall length also includes the attachment and non-working sections.

Can a rotary hammer operate continuously at its maximum diameter?

The maximum diameter is generally a limiting capability. For repeated work, check the manufacturer’s recommended or optimum range and follow the duty cycle.

How should core-bit size be selected for a pipe?

Measure the actual outside diameter of the pipe or passing component and add the clearance required by the installation method. Do not select solely by the product’s nominal description.

Can every core bit be used handheld?

No. Certain diameters, materials and systems require a drilling rig, specific speed, cooling or protective devices. Follow the permissions stated by the tool and core-bit manufacturers.

Should a narrow or wide chisel be selected?

A narrow chisel concentrates impact and is useful for local breaking of hard material. A wide blade covers a larger area and suits layer removal, but generally penetrates less deeply.

Is a longer chisel always more convenient?

No. Extra length improves reach but can reduce control and increase bending load. Select a length sufficient for the job without unnecessary excess.

Can an adapter solve every incompatibility?

No. An adapter does not change the tool’s permitted diameter, speed, power or operating mode. Use only combinations permitted by the manufacturer.

Next article: How to choose the correct drill bit or masonry bit for the material and job.