316 (A4) · Class 4.6
Coach Screws (Lag Screws)
Hex coach screws (lag screws) for heavy duty timber fixing, like ledgers, posts, beams and pergolas, and into masonry with a wall plug.
About the Coach Screws (Lag Screws)
Hex coach screws, also called lag screws, are heavy duty screws for fixing timber to timber, like ledgers, posts, beams and pergola frames, and into brick or concrete with a wall plug. They come zinc plated or hot dip galvanised (class 4.6 to AS 1393), or in 316 stainless steel (DIN 571), from M6 to M20 and up to 300mm long. Choose the finish, size and length above; the guide below covers pilot hole sizes and fitting.
Also called lag screws, lag bolts or hex head timber screws.
Features
- Hex drive coach/lag screw
- Class 4.6 to AS1393
- 316 stainless option to DIN 571
- Zinc, galvanised and stainless finishes
- Coarse thread for timber
Applications
- Deck ledgers, posts and beams
- Pergola and carport frames
- Fencing and landscaping timber
- Fixing into brick or concrete with a wall plug
What coach screws (lag screws) are for
A coach screw (also called a lag screw or lag bolt) is a heavy duty screw with a hex head, a plain shank and a coarse thread that tapers to a gimlet point. It fixes timber to timber, steel brackets to timber, and, with a wall plug, timber and fittings to masonry and concrete. Common uses are decks, pergolas, fencing and posts, farm work and general building.
Coach screw pilot hole sizes
Always drill a pilot hole or the timber may split. Drill half the screw diameter in softwoods such as pine, and three quarters of the diameter in hardwoods such as merbau. Drill the hole in the fixture (the part being fixed) 1mm larger than the screw so it passes through freely.
Hex coach screws: pilot holes and fixture hole, with socket sizes and lengths for galvanised AS 1393 coach screws (316 stainless DIN 571 heads can differ). Tap a number to show it in the selector above.
Zinc, galvanised or stainless coach screws?
Hobson's coach screw guide (Correct use of a Coach Screw) gives the finish for each use:
- Zinc plated: indoor use.
- Hot dip galvanised: moderately corrosive outdoor use, such as fencing, posts and farm work.
- 316 stainless: highly corrosive and marine conditions, and use in treated timber.
How to fit a coach screw
- Drill the fixture hole 1mm larger than the screw, then the pilot hole in the timber to the size in the table.
- Put a washer under the head so it does not dig into the timber.
- For large screws in hardwood, dip the thread in grease or lanolin to ease driving.
- Drive with a socket or spanner until the washer is firm against the timber. Do not over-tighten.
- Into masonry or concrete, use a wall plug of the right size and follow its hole size and load guidance.
Coach screws in Adelaide
Allmat supplies coach screws, coach bolts, washers and timber connectors, with the timber, to builders, carpenters and fencers across Adelaide and South Australia. Add them to a quote with the rest of your list, and we will price the lot.
Coach screws for decks, pergolas, fencing and framing
Coach screws in zinc, galvanised and 316 stainless, with washers, bolts and brackets, are available to order from Allmat for builders, carpenters, fencers and trade across Adelaide and South Australia, with the timber to go with them. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.
Goes with
Questions
What size pilot hole for an M10 coach screw?
5mm in softwood such as pine, and 7.5mm in hardwood such as merbau. Drill the fixture hole 11mm.
Do coach screws need a pilot hole?
Yes. Without one the timber is likely to split. Drill half the screw diameter in softwood and three quarters in hardwood.
What socket fits a coach screw?
For our galvanised coach screws, M6 takes a 10mm socket, M8 13mm, M10 16mm, M12 18mm, M16 24mm and M20 30mm. Stainless DIN 571 heads can differ, so check the size.
Is a coach screw the same as a coach bolt?
No. A coach screw has a hex head and a wood thread and screws into timber. A coach bolt (cup head bolt) has a domed head and a machine thread and goes right through with a nut.
Is a lag screw the same as a coach screw?
Yes, in everyday use. Lag screw and lag bolt are other names for a hex head coach screw like these. Hobson also files a headless double-ended screw (BSW machine thread one end, wood thread the other) under lag screws; that one is on our double-ended screws page.
Which coach screws for treated pine?
316 stainless. Hobson's coach screw guide recommends 316 stainless coach screws for use in treated timbers, as well as for highly corrosive and marine conditions. That advice is for coach screws: for decking screws, Hobson lists its 304 stainless self-embed head Type 17 screw as suitable for treated pine (see our batten and decking screws page).
Where can I buy coach screws in Adelaide?
Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.
Coach Screws (Lag Screws): sizes and finishes we supply
111 lines by type and finish. Pick one above for its product code and pack sizes.
| Type | Finish | Sizes | Lengths | Lines |
|---|---|---|---|---|
| Hex coach | Galvanised | M6, M8, M10, M12, M16, M20 | 25 to 300 (15 lengths) | 47 |
| Hex coach | 316 Stainless | M6, M8, M10, M12, M16 | 30 to 180 (10 lengths) | 31 |
| Hex coach | Zinc Plated | M6, M8, M10, M12 | 25 to 200 (12 lengths) | 31 |
| Countersunk | 316 Stainless | M8, M10 | 140 | 2 |
Data sheets and documents
The documents for the product you choose are listed with the selector above. Here is every Coach Screws (Lag Screws) document from Hobson Engineering.
All Coach Screws (Lag Screws) documents (14)
Data sheets and technical data (6)
Did You Know flyers (3)
Need them in bulk?
Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.
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