You’re restoring an old radio, building a wooden box, or mounting a hinge flush with the surface – and you need screws that sit perfectly flat. These slotted countersunk head machine screws are made from A2 stainless steel, so they won’t rust, stain, or corrode over time. The 90° countersunk head sinks into a pre‑drilled conical hole, leaving a smooth, flush finish that won’t snag or stick out. Choose from tiny M1.6 all the way up to M4, with overall lengths from 4mm to 50mm (including the head). The classic slotted drive gives you full control with a standard flathead screwdriver. Use them for furniture, marine hardware, automotive trim, or any project where a flush surface matters.
1. Do I need to countersink the hole for these screws to sit flush?
Yes – for the head to be perfectly flush with (or slightly below) the surface, you must drill a matching 90° countersink hole. If you drive them into a straight hole, the head will sit proud. Use a countersink bit the same size as the screw head. For soft wood, you can sometimes tap the head in with a hammer, but proper countersinking looks much better.
2. What’s the difference between A2 stainless and regular steel?
A2 stainless (also called 304) contains chromium and nickel, which form a passive layer that prevents rust. Regular carbon steel will rust quickly outdoors or in damp conditions. A2 is also non‑magnetic (or weakly magnetic), food‑safe, and resistant to many chemicals. It’s the standard choice for outdoor furniture, marine use, and kitchens.
3. Why choose slotted drive over Phillips or hex?
Slotted drives are the original screw drive – simple, easy to clean, and works with any flathead screwdriver. They’re preferred for restoration work (antique furniture, vintage electronics) where authenticity matters, and for situations where you need to control torque precisely without cam‑out. However, they can slip if the screwdriver isn’t the exact width – so use a properly fitted bit.
4. Can I use these screws with a nut, or do they need a tapped hole?
Both. You can thread them into a pre‑tapped hole of the same metric size (e.g., M3 thread into an M3 tapped hole), or pair them with a standard metric nut (M1.6, M2, M2.5, M3, or M4 nut). They are machine screws – not self‑tapping. For wood, you’d need a threaded insert or a nut on the back.
5. How do I measure the length of a countersunk screw correctly?
For countersunk screws, the overall length includes the head. Place the screw on a ruler with the head flat against the zero mark – measure to the tip. This is different from pan head or round head screws, where length is usually measured under the head. Our lengths (4mm–50mm) are overall lengths including the head.
6. Are these screws strong enough for outdoor furniture?
Absolutely – A2 stainless is ideal for outdoor furniture, garden planters, and boat fittings. They resist rain, salt spray (in moderate amounts), and temperature changes. For continuous underwater use or high‑chlorine pools, consider A4 (316) stainless, but for general outdoor DIY, A2 is perfect.
