the Walnut Diary

I picked up a couple of boxes of screws for a trim project at my local Cassell’s Building Supplies in Crosby, Ontario. I bought a box of 3/4″ #5 screws and another of 1″ #6’s. To turn the screws I bought a yellow Robertson bit and a green one for the #6’s, assuming that one of the screws would work well in the flexible door moulding I was installing.

The yellow bit turned 10 degrees when I fitted it into a #5 screw, and thus had no holding ability for the small screw, which immediately fell off. I have used boxes of #5 on cabinets and hinges, and I realized that something was seriously amiss.

The green bit wouldn’t begin to fit into the #6 screw. On examination, it was almost the size of the red Robertson I found in a pocket.

Determined to stop the northern breeze from entering our kitchen, I took a #6 screw and headed for the auto shop where I found a S1 square bit in a wrench set which is a perfect fit for the #6. It held the screw well and twisted half a box of them into the surrounding trim without event, though the shaft of the S1 required the services of a twist drill rather than an impact driver.

I photographed the product codes on the offending yellow and green bits, but Amazon and hence Google found no use for the numbers. So I asked AI.

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The number sequence 6 20535 07140 9 is a UPC (Universal Product Code) for a specific model of square screwdriver bit set, likely identifying a product from a brand such as VESTTIO or a similar tool manufacturer. 

Based on typical product descriptions associated with similar UPCs and standard industry practices, this code likely corresponds to:

• Type: Square head (also known as Robertson drive) screwdriver bits.
• Material: Often made from S2 tool steel for durability.
• Shank: Commonly a 1/4-inch hex shank, compatible with most drills, impact drivers, and power screwdrivers.
• Features: Likely includes a magnetic tip to hold screws securely. 

The number “6” at the beginning of the sequence confirms it as a standard 12-digit UPC used for retail tracking. The subsequent numbers identify the manufacturer and the specific item for inventory purposes.

4 sites

• Square Head Screwdriver Bit Set 10PCS SQ2 1/4 Inch Hex Shank 6 …Product details * About this Product. See more. * Top highlights. Brand. VESTTIO. Item length. 6 Inches. Material. S2 Steel. Finis…Amazon.ca
• Screwdriver Bits Square Recess 6″ | Stay SharpIndustrial quality, made for impact drivers with special tempered S2 spring steel. The reduced, rounded shank improves balance and…EAB Tool Company
• Square Screwdriver Bits – Grainger Industrial SupplySquare screwdriver bits (also known as Robertson bits) have a four-sided, flat-edged tip that fits into screwheads with a square r…Grainger

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The bit is yellow in colour, but is too small to hold and turn a #5 Robertson screw, the purpose for which I bought it. I also bought a green Robertson bit, which is far to large to fit a #6 Robertson screw. I eventually found a S1 bit in a tool kit which turned the #6 Robertsons effectively.

The issues you experienced are due to using incorrectly sized bits for the screw gauges (sizes)

. Different Robertson (square) bits are color-coded to match specific screw sizes. 

Here is a breakdown of the standard Robertson bit color-coding and sizing system:

Color Code	Size #	Fits Screw Sizes
Yellow	#0	#3, #4
Green	#1	#5, #6, #7
Red	#2	#8, #9, #10
Black	#3	#12, 1/4″

Why your bits didn’t work

• Yellow bit: This is a #0 size bit, designed for smaller #3 and #4 screws. It was correctly too small for your #5 screws.
• Green bit: This is a #1 size bit, designed for screw sizes #5, #6, and #7. It should have worked for your #6 screw, but it might have been an off-brand, square-drive bit without the proper Robertson taper, which can cause poor fit.
• S1 bit: The “S1” designation on the bit from your tool kit indicates a Square #1 size. This is the correct size for a #6 screw, which explains why it worked effectively. 

For future reference, ensure you match the color code or number designation (S1, S2, etc.) to the appropriate screw size to prevent stripping screws or damaging the bit. 

9 sites

• Robertson screw – WikipediaA Robertson screw, also known as a square screw or Scrulox, is a type of screw with a square-shaped socket in the screw head and a…Wikipedia
• How to choose the right screwdriver bit to fit your screw headFeb 19, 2019 — Choose the bit size that fills the screw head entirely. A bit that is too big or too small will not seat properly, and…EAB Tool Company
• How to deal with Square Drive vs. Robertson Screws?Oct 3, 2018 — Although the terms “square drive” and “Robertson” are often treated as the same in catalogs, the difference (as I under…Home Improvement Stack Exchange

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The green bit I purchased recently is too large for #6 screws. In fact, it is almost the size of the red Robertson bit.

The issue you are encountering suggests that the green bit you purchased might be a generic 

“square drive” bit rather than a true “Robertson” bit, or it may be an incorrectly sized or mislabeled product. 

Here’s why:

True Robertson vs. Generic Square Drive

• True Robertson bits (patented by the inventor, a Canadian) and their corresponding screws feature a slight tapered square socket and bit. This design provides a very secure, wobble-free fit that resists cam-out (slipping out) and can often hold the screw on the tip without needing magnetic properties.
• Generic “square drive” bits and screws have parallel sides in the square recess. These often have a looser, “sloppy” fit, which can lead to the problems you are experiencing. 

Sizing Discrepancy

A standard 

#1 Green Robertson bit is designed to fit screw sizes #5, #6, and #7. Its typical range is about 0.090–0.091 inches. A 

#2 Red bit is larger, for screw sizes #8, #9, and #10, with a range of 0.111–0.1126 inches. 

• Robertson Driver Bits$1.57
• Dynaline Color Coded Bits$2.69

If your green bit is almost the size of a red one, it is physically too large for a #6 screw. The bit from your original tool kit marked “S1” likely refers to a standard #1 square bit, which happened to have a proper fit or the necessary taper for your specific #6 screws. 

To ensure a proper fit in the future, it is best to:

• Purchase genuine Robertson bits from reputable hardware suppliers (such as those at Lee Valley Tools) who specify their bits are genuine and tapered.
• Visually test the fit of the bit in the screw head before use to ensure a snug connection.