Flat Head Screwdriver Size Guide

A flat blade is sized by two numbers, not one: the width of the tip and its thickness. This is the complete list of 25 flat screwdrivers in the range, ordered by blade width, with the Teng part number for each.

Both numbers matter, and thickness is the one people ignore

Width determines how much of the slot the blade spans; thickness determines how much of the slot depth it fills. A blade that is the right width but too thin sits in the top of the slot and rolls the edges over as soon as it is loaded, because all the force is bearing on a fraction of the available metal. That is why the range carries several thicknesses at the same width — a 6.5 mm blade at 1.2 mm and the same width at a different thickness are for different screws, not a duplicated size.

How to size a blade to a screw

Choose the widest blade that fits the slot without overhanging the head, and the thickest that will enter the slot to its full depth. Overhang is the more visible error: as soon as the driver tilts, an overhanging blade digs into whatever the screw is holding down, and on a finished surface that mark is permanent. An undersized blade is quieter but more damaging, because it destroys the slot and leaves you with a screw nothing will grip.

All 25 sizes

Blade width Blade thickness Blade length Handle size Hex bolster Teng part number
2.5 mm 0.4 mm 50 mm S No MD914N
2.5 mm 0.5 mm 75 mm S No MD915N
3.0 mm 0.5 mm 75 mm S No MD920N
3.0 mm 0.5 mm 100 mm S No MD920N1
3.5 mm 0.6 mm 75 mm S No MD916N
3.5 mm 0.6 mm 100 mm S No MD916N1
3.5 mm 0.6 mm 150 mm S No MD916N2
4.0 mm 0.8 mm 100 mm S No MD917N
4.0 mm 0.8 mm 150 mm S No MD917N2
5.5 mm 1.0 mm 75 mm M No MD922N
5.5 mm 1.0 mm 125 mm L Yes MD931N
5.5 mm 1.0 mm 150 mm M No MD923N
5.5 mm 1.0 mm 200 mm M No MD923N1
6.5 mm 1.2 mm 38 mm XS No MD928N
6.5 mm 1.2 mm 100 mm L No MD928N1
6.5 mm 1.2 mm 100 mm M No MD928N4
6.5 mm 1.2 mm 100 mm L Yes MD932N
6.5 mm 1.2 mm 150 mm L No MD928N2
6.5 mm 1.2 mm 150 mm L Yes MD932N1
6.5 mm 1.2 mm 150 mm M No MD928N5
6.5 mm 1.2 mm 200 mm M No MD928N6
6.5 mm 1.2 mm 200 mm L No MD928N3
8.0 mm 1.2 mm 150 mm XL Yes MD934N
10.0 mm 1.6 mm 200 mm XL Yes MD935N
10.0 mm 1.6 mm 200 mm XL No MD930N

Where this list comes from

Every row is read from the live Teng Tools USA catalogue on the day this page was generated — product record, part number and size taken from the record itself, never transcribed from a printed catalogue or inferred from a pattern. Blade width, thickness and length are read from each product record. Handle size and hex bolster are listed where the record states them. A size that has been discontinued disappears from this list rather than lingering as a part number you cannot order, which is the failure mode of every static spec sheet.

What the hex bolster is for

Some drivers carry a hexagonal collar where the blade meets the handle. It is there so a spanner can be put on the driver, which multiplies the torque available far beyond what a hand can apply to a grip — the correct tool for a large, seized slotted screw where the alternative is destroying the head. It also means those drivers are built to take that load throughout; putting a spanner on a driver without a bolster twists the blade in the handle instead.

The full range is in screwdrivers; bit versions are in bits and drivers.