Free tool · Australian units

Fixings Finder

Pick what you are fixing into and the fixing itself. Get the pilot hole, plug, masonry bit, hole depth and SDS bit in millimetres.

Data checked 8 September 2026 · No sign-up · Feeds rotary hammers, drills, impact drivers

Step 1

What are you fixing into?

Always pre-drill within 25 mm of a board end and for anything above 14g. Type 17 self-drilling tips manage most hardwoods up to 10g, but in dense species (spotted gum, ironbark, jarrah) pre-drill 0.5 to 1 mm under the shank so the screw neither snaps nor splits the board. Use stainless (316 near the coast) or Class 4 coated screws outdoors.

Step 2

Which fixing?

Step 3

What size?

Your sizes

10g wood screw (4.8 mm) into hardwood

Pilot hole

3.5mm

hardwood size

Clearance hole

5.5mm

in the top piece

Countersink

9.9mm

head diameter

Drill mode

Rotary

Brad-point or HSS bit, plus a countersink for decking

Very dense species (spotted gum, ironbark, jarrah): go up 0.5 mm on the pilot and drive at low speed so the screw does not shear.
Pilot depth is the full length of the thread. Mark the bit with tape at the screw length.
An impact driver drives 10g and larger screws faster and with less wrist strain than a drill on a clutch setting.

Best impact drivers for the job→

How it works

Method and assumptions

Timber pilot holes are sized from the screw's core diameter: about the core in softwood so the thread still bites, and a touch larger in dense Australian hardwoods so the screw neither snaps nor splits the board. The clearance hole in the top piece matches the shank, so the two pieces pull together instead of jacking apart.

Masonry holes match the plug or anchor: a 6 mm plug needs a 6 mm hole, a 10 mm Dynabolt needs a 10 mm hole. Depth is the plug or anchor length plus a margin for dust, so the fixing never bottoms out before it is tight.

Drilling mode follows the material: rotary for timber, hammer for solid brick, an SDS-plus rotary hammer for concrete, and rotary only for hollow brick, blocks and tiles, where hammer action shatters the material.

Sizes come from fastener manufacturer and supplier tables and are a starting point, not an engineering specification. For anything structural, the anchor manufacturer's datasheet for your exact product governs hole size, embedment depth and load. Test a fixing in an offcut or a hidden spot first.

Reference charts

The tables behind the finder

All sizes in millimetres. Pilot holes are for the piece the thread grips; clearance holes are for the piece the screw passes through. Hardwood pilots are ITW Proline's published sizes; softwood pilots follow the 60 to 70% of shank rule, rounded to bits you can buy; clearance and head sizes come from the shared imperial gauge table.

Wood screws by Australian gauge

Gauge	Diameter	Pilot, softwood	Pilot, hardwood	Clearance	Countersink
4g	2.85	1.5	2.0	3.0	6.0
6g	3.50	2.0	2.5	4.0	7.1
8g	4.20	2.5	3.0	4.5	8.7
10g	4.80	3.0	3.5	5.5	9.9
12g	5.50	3.5	4.5	6.5	11.1
14g	6.30	4.0	5.0	7.0	12.7

Coach screws

Size	Pilot, softwood	Pilot, hardwood	Clearance	Spanner
M6	3.0	4.5	7.0	10 mm
M8	4.0	6.0	9.0	13 mm
M10	5.0	7.5	11.0	17 mm
M12	6.0	9.0	13.0	19 mm

Wall plugs

Plug	Masonry bit	Hole depth	Screw	Usual colour (AU)	UK chart colour
5 mm x 25	5	35	4g to 6g (2.9 to 3.5 mm)	white (Ramset)	yellow
6 mm x 35	6	45	8g to 9g (4.2 to 4.5 mm)	red (Ramset)	red
7 mm x 35	7	45	10g to 12g (4.8 to 5.5 mm)	green (Ramset)	brown
8 mm x 50	8	60	14g to 16g (6.3 to 6.8 mm)	blue (Ramset)	blue on Rawlplug UNO; classic UK blue is 10 mm
10 mm x 50	10	60	14g to 18g (6.3 to 7.5 mm)	not colour coded (Ramset RamPlug nylon anchor)	blue (classic) or grey (Rawlplug UNO)

Colour coding is not standardised between brands in Australia. The millimetre size on the packet is the only figure to trust.

Sleeve anchors (Ramset DynaBolt Plus)

Size	Drill	Bracket hole	Hole depth	Embedment	Thread	Spanner	Torque (concrete)	Torque (brick)
6 mm	6	8	30 to 60 by length	25	M4.5	–	10 Nm	–
8 mm	8	10	50 to 75 by length	35	M6	10 mm	15 Nm	10 Nm
10 mm	10	12	50 to 85 by length	45	M8	13 mm	35 Nm	15 Nm
12 mm	12	15	70 to 95 by length	50	M10	17 mm	55 Nm	15 Nm
16 mm	16	19	80 to 120 by length	65	M12	19 mm	85 Nm	–
20 mm	20	24	100 to 155 by length	85	M16	24 mm	165 Nm	–

Figures from Ramset datasheets. Hole depth grows with anchor length; spanner sizes are the ISO hex for the thread, which Ramset does not publish.

Wedge anchors (Ramset TruBolt)

Size	Drill	Bracket hole	Hole depth	Embedment	Thread	Spanner	Torque (concrete)	Torque (brick)
M6	6	8	55 to 75 by length	32	M6	10 mm	10 Nm	–
M8	8	10	65 to 75 by length	54	M8	13 mm	20 Nm	–
M10	10	12	80 to 100 by length	72	M10	17 mm	35 Nm	–
M12	12	15	90 to 125 by length	86	M12	19 mm	50 Nm	–
M16	16	19	125 to 145 by length	115	M16	24 mm	155 Nm	–
M20	20	24	160 to 200 by length	145	M20	30 mm	355 Nm	–

Figures from Ramset datasheets. Hole depth grows with anchor length; spanner sizes are the ISO hex for the thread, which Ramset does not publish.

Screw-bolts (Ramset AnkaScrew)

Size	Drill	Bracket hole	Hole depth	Embedment	Thread	Spanner	Torque (concrete)	Torque (brick)
5 mm	5	7	≥ 30	25	5 mm screw-bolt, flanged hex	–	–	8 Nm
6 mm	6	8	≥ 60	45	6 mm screw-bolt, flanged hex	10 mm	–	10 Nm
8 mm	8	10	≥ 75	60	8 mm screw-bolt, hex	13 mm	–	10 Nm
10 mm	10	12	≥ 80	75	10 mm screw-bolt, hex	15 mm	–	15 Nm
12 mm	12	15	≥ 100	90	12 mm screw-bolt, hex	16 mm	–	15 Nm

Figures from Ramset datasheets. Hole depth grows with anchor length; spanner sizes are the ISO hex for the thread, which Ramset does not publish.

SDS-plus bit sizes

Stocked at Bunnings: 5, 6, 6.5, 8, 10, 12, 14, 16, 18, 22, 24, 28 mm

Trade suppliers only: 4, 5.5, 7, 13, 20, 25 mm

SDS-max starts at 16 mm at Bunnings and takes over for big holes; SDS-plus shanks are 10 mm, SDS-max 18 mm.

Drilling mode by material

Material	Mode	Bit	Notes
Softwood: pine, treated pine, plywood, MDF	Rotary (hammer off)	HSS twist or brad-point bit	Small screws (4g to 6g) usually drive into pine without a pilot. Pre-drill within 50 mm of a board end to stop splitting. Batten and Type 17 screws are self-drilling in softwood.
Hardwood: merbau, spotted gum, blackbutt, jarrah, ironbark	Rotary (hammer off)	Brad-point or HSS bit, plus a countersink for decking	Always pre-drill within 25 mm of a board end and for anything above 14g. Type 17 self-drilling tips manage most hardwoods up to 10g, but in dense species (spotted gum, ironbark, jarrah) pre-drill 0.5 to 1 mm under the shank so the screw neither snaps nor splits the board. Use stainless (316 near the coast) or Class 4 coated screws outdoors.
Solid brick (clay or concrete)	Hammer drill or SDS-plus	TCT masonry bit, or an SDS-plus bit in a rotary hammer	Drill into the brick body, not the mortar, for anything heavy. Start on rotary to seat the bit, then switch to hammer. Blow or vacuum the dust out before the plug goes in.
Mortar joint between bricks	Rotary or light hammer	TCT masonry bit	Mortar is weaker than the brick and crumbles under heavy hammer action, so use it only for light fixings, keep the hole no wider than the joint, and use a longer plug. For anything that carries weight, move the hole into the brick.
Concrete: slab, footing, precast panel	SDS-plus rotary hammer	SDS-plus masonry bit	A hammer drill gets through a slab slowly; an SDS-plus rotary hammer does it in seconds and drills a rounder hole, which anchors need. Clean the hole with a blower or brush before setting an anchor; dust halves the hold.
Hollow brick, concrete block or Hebel (AAC)	Rotary only (hammer off)	TCT masonry bit on rotary	Hammer action breaks the thin webs of hollow bricks and turns Hebel to powder: CSR says to use a standard drill, not a rotary hammer, with the hammer setting off. Use plugs and anchors rated for hollow material (RamPlug, AnkaScrew, the hex-bolt DynaBolt at reduced torque) or a chemical anchor with a sieve sleeve; plain sleeve and wedge anchors need solid material to expand against.
Rendered masonry	Rotary through the render, then hammer	TCT masonry bit or SDS-plus	Render is a skin. Go through it on rotary so it does not crater, then hammer into the brick or block behind. Size the plug and the hole depth for the masonry, not the render.
Plasterboard (gyprock) with no stud behind	No pilot for self-drilling anchors	Self-drilling plasterboard anchor, or a hole to suit a toggle anchor	Self-drilling anchors (Ramset WallMate style) drive straight into 10 and 13 mm board with a #2 Phillips bit, no pilot. Toggle anchors state their hole size on the packet. Anything heavy, from a TV bracket to a towel rail you will lean on, goes into a stud or noggin; find it first.
Ceramic or porcelain tile	Rotary only, slow speed	Spear-point tile bit (ceramic) or diamond core bit with water (porcelain); tape the spot	Masking tape stops the bit skating; drill slowly and never on hammer, which cracks tiles. Once through the tile, switch to a masonry bit with hammer for the wall behind, sized for the plug, and keep holes at least 30 mm from tile edges.
Steel: RHS, angle, brackets, sheet	Rotary, low speed	HSS or cobalt twist bit with cutting fluid	Tek (self-drilling) screws need no pilot up to their rated thickness. For bolts, drill the clearance size (M8 needs 9 mm, M10 needs 11 mm) and deburr the hole.

Fixings Finder — Frequently Asked Questions

What size drill bit do I need for an 8g screw?+

An 8g wood screw is about 4.2 mm across the thread. Drill a 2.5 mm pilot in softwood such as pine, and 3.0 mm in hardwood such as merbau or spotted gum. If the screw passes through a top piece first, drill that piece at 4.5 mm so it pulls down tight.

What size drill bit for a 6 mm wall plug?+

A 6 mm plug needs a 6 mm masonry bit and a hole about 10 mm deeper than the plug, so around 45 mm for a 35 mm plug. Ramset's red 6 mm plug is rated for 8g to 9g screws (4.2 to 4.5 mm). Colours differ between brands and countries (UK charts use red for 6 mm too, but blue for 10 mm where Ramset's blue is 8 mm), so go by the millimetre size printed on the packet.

What drill bit do I use for a 10 mm Dynabolt?+

Sleeve anchors are drilled to their own nominal size: a 10 mm DynaBolt Plus takes a 10 mm masonry or SDS-plus bit, needs at least a 50 mm deep hole (deeper for longer anchors: the anchor length plus one diameter), carries an M8 thread, and is torqued to about 35 Nm in concrete or 15 Nm in brick. Clean the dust from the hole before it goes in.

Do I need to pre-drill merbau or spotted gum decking?+

Yes for dense species and always near board ends. Type 17 self-drilling decking screws manage most hardwoods up to 10g, but spotted gum, ironbark and jarrah split at the ends and snap screws, so pre-drill 0.5 to 1 mm under the shank (about 3.5 mm for a 10g screw), within 25 mm of every end, and countersink. Use 10g for standard boards, 12g for 140 mm boards, and stainless or Class 4 coated screws outdoors.

Can I use hammer mode in hollow brick or Hebel?+

No. Hammer action breaks the thin webs of hollow bricks and blocks and turns Hebel to powder. Drill on rotary only, and use hollow-wall anchors, chemical anchors with sieve sleeves, or Hebel-specific screws instead of sleeve or wedge anchors, which need solid material to expand against.

What is the difference between a pilot hole and a clearance hole?+

The pilot hole is drilled in the piece the thread grips; it is smaller than the screw so the thread cuts into the timber. The clearance hole is drilled in the piece the screw passes through; it is the shank diameter or a little more, so the head pulls the top piece down instead of the thread holding it away.

Which SDS-plus bit sizes are common in Australia?+

Bunnings stocks SDS-plus bits in 5, 6, 6.5, 8, 10, 12, 14, 16, 18, 22, 24 and 28 mm. Sizes such as 4, 5.5, 7, 13, 20 and 25 mm exist from Sutton and Bosch but come from trade suppliers, so a 7 mm green plug is usually drilled with a 7 mm TCT masonry bit in a hammer drill. SDS-max starts at 16 mm and takes over for big holes.

You'll need

Best SDS-plus rotary hammers for masonry

For brick, block and concrete, the rotary hammer is the tool that makes the hole sizes above quick and round.

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