Diamond Saw Blade Arbor Sizes Explained: 7/8" Arbor, 5/8"-11 Thread & Reducer Bushings

"Will this blade fit my machine?" It's one of the questions we get most often — and the answer always comes down to two numbers: the blade diameter and the arbor (the mounting hole or thread). Here's everything you need to know to match any diamond tool to your machine.

The Common Arbor Sizes

• 7/8" (22.23 mm) — the standard arbor for angle grinders. Every common grinder blade size — 4-1/2" (115 mm), 5" (125 mm), 6" (150 mm), 7" (180 mm), and 9" (230 mm) — uses this hole. If you're buying a blade for an angle grinder, 7/8" is almost certainly what you need.

• 1" (25.4 mm), 20 mm, and 30 mm — found on tile saws, masonry table saws, walk-behind saws, and high-speed cut-off saws running blades 12" (300 mm) and up. The arbor size your machine needs is stamped on the machine's blade flange — check there before you order.

The Reducer Bushing: One Blade, Two Machines

Many larger blades are marked with a dual arbor size — for example "1"/20 mm". These blades have the larger bore and come with a press-in reducer bushing (also called a reducer ring) that steps the hole down to the smaller size. That one blade then fits two different machine types.

The critical detail: the bushing must sit flat and fully pressed in, flush with the blade core on both sides. A bushing that sits proud or crooked puts the blade off-center, causing vibration, wobble, and premature wear — and at full rpm, an out-of-balance blade is a safety hazard. Seat it properly before the blade ever touches the flange.

A wobbling blade is more than a wear problem — see our 10 angle grinder safety rules for what to check before every mount.

5/8"-11 — The Threaded Hub

Some tools skip the arbor hole entirely. Tools with a 5/8"-11 threaded hub — mortar rakes, grinding cup wheels, dry core bits, and sanding backing pads — screw directly onto the angle grinder's spindle, with no flange and no lock nut needed. The advantages:

• Faster tool changes — spin it on, spin it off, no wrench juggling
• No lost lock nuts rolling around the jobsite
• Automatic centering — the thread aligns the tool perfectly on the spindle every time

A good example is the PRODIAMANT Carbide Mortar Rake, which threads straight onto any standard 5/8"-11 angle grinder spindle for mortar joint cleaning — no adapter, no flange hardware.

Curious what that tool is actually used for? Our tuckpointing guide to removing old mortar joints walks through the whole job step by step.

Checklist Before You Buy

1. Maximum blade diameter your machine accepts — never mount a larger blade than the guard is designed for.
2. Arbor size or spindle thread — 7/8" arbor for grinder blades, 5/8"-11 for threaded tools, and check the flange stamp on saws.
3. Rpm rating — the blade's maximum rated speed must be higher than your machine's no-load speed. This one is non-negotiable.

With those three numbers checked, any blade in our lineup — from the Tile Leopard to the Turbo Panther — will mount right the first time.

Buying your very first blade? Our first diamond blade buying guide covers rim types, sizing, and the classic beginner mistakes.