Hole Saw for Standard Monotubs - 51mm / 2"

A 2" (51 mm) bi-metal hole saw — the universal monotub size. This is the hole everyone drills first: big enough for the standard gas-exchange filter patch, the right diameter for a snap-in thermometer/hygrometer, and the size all standard hole plugs are made for. Ships with a quick-change hex shank arbor so it goes straight into any cordless drill.

The single most useful size for monotub building

Why 2" is the standard monotub hole

If you only buy one hole saw, this is the one. A 51 mm hole is what virtually every monotub tutorial recommends, and the whole ecosystem of monotub accessories is built around it:

• It fits the standard filter patch — Standard Monotub Filters 65 mm — Self-Adhesive 12-Pack are 65 mm and seal cleanly around a 51 mm hole with a comfortable adhesive margin on all sides.
• It fits a snap-in thermometer/hygrometer — the Hygrometer & Thermometer for Standard Monotub is designed to press into a 2" hole, replacing a filter patch with a live readout when you want to track climate during fruiting.
• It fits standard hole plugs — the Hole Plugs for Standard Monotubs — 6-Pack (2") slot straight in. Close holes during colonisation, then open the tub up when you switch to fruiting.
• Standard cultivation guidance — most monotub teks call for 2" holes specifically. You can find a 2" filter, a 2" plug, and a 2" thermometer port from any mycology supplier.

Build a 35-60 L monotub in 10 minutes

A standard layout for a 35–60 L tub uses six 2" holes around the perimeter:

• Mark a line — 8 to 9 cm from the base of the tub. That keeps the holes just above where the substrate level will sit.
• Two holes per long side, one per short side — six holes total, evenly spaced.
• Drill in reverse, slowly — reverse rotation shaves the plastic; forward rotation bites in and cracks brittle tubs. Take it easy on the trigger.
• Brace the wall — press a scrap block of wood behind each spot. Stops the saw from snatching when the teeth break through.
• Clean burrs — trim leftover plastic with a sharp blade or sandpaper so filter patches sit flat and seal completely.
• Stick the patches — apply a 65 mm filter patch centred over each hole. Press from the centre outwards to push out air bubbles.

What's in the box

• 1× bi-metal hole saw — 51 mm (2") cutting diameter, HSS teeth on carbon-steel body.
• 1× quick-change hex shank arbor — with pilot drill bit. Fits standard 1/4" hex chucks and three-jaw drill chucks.

Tips for a clean cut

• Cordless drill, low speed — high RPM melts plastic and gums up the teeth. Low and slow is faster overall.
• Reverse for plastic, forward for metal/wood — this isn't a typo. Polypropylene monotubs crack easily with forward-spinning teeth; reverse rotation prevents this.
• Don't lean — let the saw do the work. Pushing harder doesn't cut faster; it overheats the teeth and warps the saw body.
• Knock out the plug — after the cut, push the leftover plastic disc out from the inside of the tub. A flat screwdriver helps if it's stuck.

Specifications

• Cutting diameter — 51 mm (2 inches).
• Material — HSS bi-metal teeth on a carbon-steel body.
• Shank — quick-change hex shank arbor included with pilot drill.
• Best for — plastic monotubs (PP, PE, HDPE), thin metal, wood.
• Pairs with filter — 65 mm self-adhesive patches.
• Pairs with thermometer — Monotub Hygrometer/Thermometer (snap-in, 2").
• Pairs with hole plugs — Monotub Hole Plugs 2" (close holes during colonisation).

Safety: Wear eye protection when drilling. Plastic chips fly at speed. Use a sturdy work surface; never drill a monotub freehand on your lap. The saw body stays hot after cutting — give it 30 seconds before touching. Keep out of reach of children.