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Robertson screws: which one, and what it should cost

By Simon Lafortune, Co-founder, Buildsavr · September 19, 2026

If you grew up building in Canada, the square drive is just what a screw looks like. P.L. Robertson patented it in Milton, Ontario in 1909, and it stayed the standard here long after most of the world settled on Phillips.

There is a practical reason it stuck. A Robertson bit holds the screw on the driver, so you can start a fastener one handed, up a ladder, in the cold. It also cams out far less, which means fewer stripped heads on a long day.

$4.18 to $11.28
same 1 lb box, six Quebec retailers, May 2026
#6 to #12
the gauge range that covers almost every job
Coating
what decides survival in treated lumber, not brand

Which Robertson screw for which job

Three things decide the screw: gauge (#6 to #12), length, and coating. Gauge and length come from the assembly. The coating comes from where it lives.

  • Drywall, #6, fine thread for steel studs and coarse for wood. Bugle head so it sits below the paper without tearing it.
  • Interior wood and framing, #8, zinc plated. The general purpose screw for anything that stays dry.
  • Subfloor, #8 x 2 1/2 in, coarse thread. Zinc is fine, the floor is inside.
  • Treated lumber and decks, #8 or #10, ceramic coated. Not zinc. See the next section.
  • Ledger and structural connections, #10 to #12 or a proper structural screw. This is the one place not to improvise.
  • Cedar, coastal air or anything you want to still look right in ten years, 305 stainless.

Treated lumber: the coating is the whole decision

Modern pressure treated lumber uses copper based preservatives. Copper in contact with plain zinc plating sets up a galvanic reaction, and the plating loses. The screw corrodes from the inside of the joint outward, where you cannot see it, and the first sign is usually a board that moves underfoot years later.

**The rule:** anything going into treated lumber is ceramic coated, hot dip galvanized, or stainless. A zinc plated screw in an ACQ deck is not a budget choice, it is a future repair.

This is also why a deck screw costs 1.5 to 2 times what the same size interior screw costs. You are paying for the coating, and it is the part that matters.

What a box costs by category

Ranges observed in major Quebec hardware stores for the most common formats, sold in a 1 lb box. Prices before tax, excluding weekly promotions.

  • Interior zinc wood screw #8 x 1 1/2 in, about $7 to $12 per lb
  • Interior zinc wood screw #8 x 2 1/2 in, about $9 to $14 per lb
  • Ceramic coated deck screw #8 x 2 1/2 in, about $14 to $22 per lb
  • Ceramic coated deck screw #10 x 3 1/2 in, about $18 to $26 per lb
  • GRK R4 multi purpose #10 x 3 in, about $26 to $38 per lb
  • GRK RSS structural 5/16 x 4 in, about $3 to $4 per screw
  • 305 stainless #8 x 2 1/2 in, about $28 to $45 per lb

The same box, 2.7x the price

This is what makes screws worth comparing at all. Below is what six retailers were charging for the same standard Robertson #8 x 2 1/2 in wood screw, roughly a 1 lb box, on 24 May 2026.

**This is an archive, not a live comparison.** These prices are not refreshed, they change weekly, and they vary by branch. For today’s number, use the app.

When a $30 per pound screw is the cheap option

GRK and Spax cost three to five times a generic deck screw, and on most of a project that is money wasted. On a few specific lines it is not.

Their case is self drilling geometry and a head that will not cam out under torque: no pilot hole, no split ends on a rim joist, no stripped head on a cold morning. On a ledger, a stair stringer, or anything structural where a failed fastener means taking the assembly apart, the labour you save is worth more than the box.

On decking boards, field framing and sheathing, a good ceramic coated screw does the same job for a fraction of the price.

How many screws a typical project takes

Rough quantities, so you buy once instead of making a trip back at full price for the last handful.

  • Basement drywall, 800 sq ft: about 5 lb of #6 x 1 1/4 in drywall screws, roughly 1 lb per 160 sq ft of board.
  • OSB subfloor 5/8 in over joists, 1,200 sq ft: about 8 lb of #8 x 2 1/2 in floor screws.
  • Shed 8 x 10 ft: about 6 lb assorted, mostly #8 x 2 1/2 in for decking and #8 x 1 1/2 in for siding.

Mistakes that cost the most

None of these are exotic. They are just expensive.

  • Zinc plated screws in treated lumber. Covered above, and it is the costliest one.
  • Buying 1 lb boxes for a job that needs eight. The per pound price on a 5 lb box is meaningfully lower.
  • Using drywall screws for framing. They are hardened and brittle, and they snap under shear.
  • Guessing the length. The rule of thumb is that the screw should reach about two thirds into the receiving member.
  • Buying screws wherever you are already standing. As the table shows, the same box runs from $4.18 to $11.28.

Frequently asked questions

Why Robertson instead of Phillips?
The square recess grips the bit, so the screw stays on the driver and you can start it one handed. It also cams out far less than a Phillips, which means fewer stripped heads and less damage to the work. P.L. Robertson patented it in Milton, Ontario in 1909, and it remained the Canadian default.
What screws should I use for pressure treated lumber?
Ceramic coated, hot dip galvanized or stainless. Never plain zinc plated. Modern treated lumber uses copper based preservatives, and copper in contact with zinc plating sets up a galvanic reaction that eats the fastener from inside the joint where you cannot see it.
How much does a 1 lb box of Robertson screws cost?
For a standard #8 x 2 1/2 in interior wood screw, we observed $4.18 to $11.28 across six Quebec retailers on 24 May 2026, for the same box, a spread of 2.7x. Ceramic coated deck screws of the same size run roughly 1.5 to 2 times that, and premium structural screws such as GRK R4 or Spax run 5 to 7 times.
GRK or Spax: which should I buy?
Either, and only where it earns the premium. Both offer self drilling geometry and heads that resist cam out, which matters on ledgers, stringers and structural connections. On decking, field framing and sheathing, a good ceramic coated screw does the same job for far less.
Should I buy the 1 lb or the 5 lb box?
If the job needs more than about two pounds, buy the 5 lb box. The per pound price is meaningfully lower, and promotions on the larger boxes are common. If you need a handful for a repair, the 1 lb box is fine.

Do not pay $11.28 for a $4.18 box

Buildsavr prices your full material list across every retailer we cover and returns the cheapest store for each line. Live in Quebec, rolling out across Canada. First comparison free.