115mm vs 125mm Cutting Discs: Which Do You Need?

Most angle grinders sold in Australia take either a 115mm (4.5 inch) or a 125mm (5 inch) disc, and the two sizes are close enough that people often ask whether it matters. It does. The disc must match your grinder's stated disc size, the guard must match the disc, and each size suits slightly different work. Here is how to choose.

First Rule: Match the Disc to the Grinder

A grinder is rated for one maximum disc size, marked on the tool and in its manual. A 115mm grinder takes 115mm discs. A 125mm grinder takes 125mm discs, and usually accepts smaller discs too, though the guard and cutting depth are designed around the full size. Never fit an oversized disc. Follow your tool maker's instructions on disc size at all times.

The easiest check is the label on your grinder or its manual. If the disc size is not marked, do not guess: check with the maker or the retailer.

The Practical Differences

115mm (4.5")	125mm (5")
Fits	The most common small grinders in Australia	Slightly larger trade grinders
Cutting depth	A few millimetres less per pass	Slightly deeper per pass
Weight and fatigue	Lighter, easier overhead	A touch heavier
Disc availability	The most widely stocked size	Widely stocked, slightly fewer options
Best for	Most home cutting and grinding	Regular trade use, faster stock removal

The real difference is modest. A 125mm disc reaches a few millimetres deeper into a cut and removes material a little faster, which matters when you cut all day. For occasional jobs around the house, a 115mm grinder usually provides enough reach for common cutting and grinding tasks. Check the grinder's size rating and disc availability before settling on a replacement.

What About the Bore?

Both sizes commonly use a 22.23mm bore, the standard fit for angle grinders sold in Australia. Our 125mm super-thin cutting disc is 125 x 22.23 x 1.1mm, so it fits standard 125mm grinders directly. Some smaller discs use other bores with a reducing ring supplied with the disc. Check the bore before buying.

Thickness Matters as Much as Diameter

For cutting rather than grinding, a thin disc cuts faster, cleaner and with less heat. Our super-thin 125mm disc is 1.1mm thick, which keeps the kerf narrow and the chipping minimal on tile and stone. Thicker discs around 2 to 3mm last longer but cut slower and remove more material, so they suit rough work rather than finished cuts.

Which Discs Does Pro Tool Box Stock?

• Pro Tool Box 125mm Super-Thin Diamond Cutting Disc: 125 x 22.23 x 1.1mm turbo rim, for porcelain, ceramic, marble, granite and stone. Available as a single disc or a 5 pack.

• Pro Tool Box Diamond Cutting Disc, 105/115/125mm: a segmented disc in three sizes, so it matches 115mm and 125mm grinders alike.

• 10 Pack Pro Tool Box 125mm Diamond Cutting Discs: ten thin turbo discs for regular tile and stone cutting.

• Glass Cutting Disc 100/115/125mm Ultra-Thin: for glass, jade and crystal as well as delicate tile.

If you own a 115mm grinder, the 105/115/125mm segmented disc in the 115 size is your fit, and the glass disc also comes in 115mm. If you own a 125mm grinder, the super-thin turbo disc is a good fit for porcelain and ceramic tile work.

Check the Full Disc Specification

Diameter is only one part of the fit. Check the bore, maximum rated speed and permitted cutting method on the disc label and in the grinder manual. The grinder's no-load speed must not exceed the disc's maximum speed. A reducing ring is only suitable when the disc maker supplies or permits it. Do not enlarge a bore or improvise a spacer to make a disc fit.

Also distinguish a cutting disc from a grinding disc. Cutting discs are thin and intended to cut with the edge. Side-loading a thin cutting disc while grinding can damage it. Use the accessory designed for the operation and keep the guard in its correct position.

Do a Test Cut First

If you are working with a new material or a new disc, make a short test cut in an offcut before committing to the finished piece. This shows whether the disc and tool combination is suitable and lets you check the finish. Mark the cut line clearly, support the material on both sides and avoid twisting the grinder as the disc exits the cut. For tile, a stable support and steady movement help reduce edge chips.

When choosing between a single disc and a pack, think about how often you cut and whether all the discs share the same size and specification. Do not buy a pack just because the per-disc price looks lower. Check the diameter, bore and thickness on each listing, then make sure the disc matches the grinder you own.

Safety Essentials

Whatever the size, keep the guard fitted and matched to the disc, check each disc for chips or cracks before use, clamp your workpiece, and wear eye, ear and lung protection. Cutting tile and stone creates silica dust, so cut wet where you can and follow local regulations on dust control. Follow your tool maker's instructions at all times.

Quick Answers

Can I put a 125mm disc on a 115mm grinder?

No. Never fit a disc larger than the grinder's rated size. The guard will not cover it and the motor is not rated for it.

Can I put a 115mm disc on a 125mm grinder?

Often yes, if the grinder's manual allows smaller discs and the bore matches, but the guard is designed for the full size. Check your tool maker's instructions.

Which size should I buy for cutting tiles?

The size your grinder takes decides it. For a 125mm grinder, the super-thin 1.1mm turbo disc is a suitable option for porcelain and ceramic. Check the listing and your grinder manual before fitting it.

Is a bigger disc a bigger cut?

Only slightly. A 125mm disc cuts a few millimetres deeper than 115mm, which matters for trade use but rarely for home jobs.

Where to Start

See the full diamond cutting disc range at Pro Tool Box. Every order is dispatched within 1-2 business days and shipping is free Australia-wide.