The flat head - also called a slotted, flat blade, or standard screwdriver - is the original screwdriver design, dating back to 15th-century Europe. A flat blade fits into a single straight slot cut across the screw head.
Flat Head Screwdriver Sizes
Flat head screwdrivers are sized by blade width and thickness. The blade should fill the full width and depth of the screw slot - too narrow and it strips; too wide and it won't seat.
| Blade Width | Blade Thickness | Screw Slot Width | Typical Use |
|---|---|---|---|
| 3.0 mm | 0.5 mm | 3 mm | Small electronics, terminal blocks |
| 4.0 mm | 0.6 mm | 4 mm | Light fixtures, switches |
| 5.5 mm | 0.8 mm | 5–6 mm | Electrical outlets, general hardware |
| 6.5 mm | 1.0 mm | 6–7 mm | Cabinet hardware, medium screws |
| 8.0 mm | 1.2 mm | 8 mm | Heavy-duty hardware, construction |
| 10.0 mm | 1.6 mm | 10 mm | Large industrial screws |
| 12.0 mm | 2.0 mm | 12 mm | Heavy machinery |
Where Flat Head Screwdrivers Are Still Used
- Electrical terminal screws - most terminal blocks still use slotted screws for quick half-turn tightening
- Set screws and adjustment screws in machinery
- Older furniture, antique hardware, and restoration work
- As a general-purpose prying, scraping, or opening tool
- Paint can lids - the flat blade doubles as a lever
For electrical work with slotted terminal screws, use an insulated flat head screwdriver rated to VDE 1000V. Standard flat heads have no electrical protection.
The Main Drawback
The flat blade can slip sideways out of the slot under torque. This makes slotted screws a poor choice for power tools and high-torque applications - which is exactly why Phillips, Torx, and other anti-slip designs were invented. But for low-torque applications like electrical terminals, the simplicity is an advantage.
Related Guides
Types of Screwdrivers: The Complete Guide
From Phillips to Torx, flat head to hex - every screwdriver type explained with sizes, uses, and selection tips.
Phillips Screwdriver: Sizes, Uses & How to Choose the Right One
PH0 to PH4 sizes explained - which Phillips head screwdriver to use and when.
Insulated Screwdrivers: VDE Standards, Ratings & Safety
VDE-rated insulated screwdrivers are mandatory for live electrical work. Standards, identification, and when you need them.