Best Flat Head Hex Bolts and Assortment Kits for Home and Workshop Projects
Flat head hex bolts are designed for applications where a low-profile, flush-style head and hex-socket drive are useful. The best choice depends on whether you need a single inch-size fastener, several lengths, or a metric assortment. The options below include stainless steel and carbon steel products, plus kits with nuts, washers, or tools. Check the thread size and how the listed length is measured before ordering.
| Product | Best For | Key Detail |
|---|---|---|
| 330-piece M3–M5 kit | Metric home and workshop use | Stainless steel screws, nuts, and washers |
| 1,700-piece M2–M5 kit | Broad metric size selection | Six lengths and alloy steel |
| 1/4-20 x 1-1/2-inch pack | Small inch-size projects | 20 stainless steel screws |
| Taiss 80-piece set | Furniture and multiple lengths | Seven listed size options |
| Biaungdo 30-piece pack | Matching black fasteners | 1/4-20 carbon steel bolts |
330-Piece M3–M5 Stainless Steel Kit
This assortment combines M3, M4, and M5 countersunk hex-socket screws with nuts and washers. The stainless steel construction is described as corrosion- and rust-resistant, and the hex socket is intended to help the tool engage during installation. A compartmented transparent storage box keeps the different pieces separated.
Best for: Buyers who need common metric sizes and the matching nuts and washers in one organized kit. It was selected for its included hardware and storage case, which can help with small repair and assembly jobs.
Limitation: The kit covers M3 to M5 sizes; choose another option if you need M2 screws or inch-thread fasteners.
1,700-Piece M2–M5 Alloy Steel Assortment
This large metric assortment lists M2, M3, M4, and M5 screws, with six lengths from 8 mm to 25 mm. It includes nuts, flat washers, lock washers, a hex key, and hex Allen wrench drill bits. The listed thread pitches are 0.4 mm for M2, 0.5 mm for M3, 0.7 mm for M4, and 0.8 mm for M5. The screws are described as alloy steel.
Best for: Repair benches and projects that require a wider range of metric diameters and lengths. It offers more size variety than the 330-piece kit.
Limitation: This is a metric set, not a substitute for 1/4-20 or other inch-thread fasteners. Confirm the required thread before choosing.
1/4-20 x 1-1/2-Inch Stainless Steel Screws
This pack contains 20 flat head hex socket screws made from 304 stainless steel, also identified as 18-8, and includes one hex key. The product name specifies a 1/4-20 thread and a 1-1/2-inch length. The listing describes the screws as fully machine-threaded and highlights corrosion resistance.
Best for: Buyers who know they need this particular inch-size fastener and want a compact pack with a hex key. Its fixed size makes it simpler to select than a mixed assortment.
Limitation: The listing’s feature text gives an unclear size description for thread pitch. Verify the 1/4-20 specification and length against your application before ordering.
Taiss 80-Piece Furniture Bolt Set
This set lists seven size options: five 1/4-20 lengths from 3/4 inch to 2 inches, plus two 5/16-18 lengths. The bolts are described as fully threaded 304 stainless steel with a black zinc plating and a hex-socket drive. A hex wrench is included, according to the product title.
Best for: Furniture assembly or repair when you need several listed lengths and both 1/4-20 and 5/16-18 sizes. It offers more inch-size choices than the single-size pack.
Limitation: The listed assortment does not cover every length in each thread size. Match the exact diameter and length to the furniture or project requirements.
Biaungdo 30-Piece Black 1/4-20 Bolts
This pack contains 30 black flat head Allen bolts made from carbon steel. The listed thread diameter is 1/4 inch, with 20 threads per inch, and the stated 2-inch screw length includes the head. The product description characterizes the material as hard and corrosion-resistant.
Best for: Buyers looking for a larger quantity of black 1/4-20 fasteners in one length. It is a straightforward option when the color and specified thread match the project.
Limitation: The 2-inch measurement includes the head, so do not assume it represents the length below the head. The pack offers one listed size.
Buying Guide: How To Choose Flat Head Hex Bolts
Do you need metric or inch threads?
Start by matching the fastener to the threaded hole, nut, or existing bolt. Metric products use sizes such as M4, while inch products may use 1/4-20 or 5/16-18. These systems are not interchangeable. For replacements, check the diameter and thread pitch or threads per inch rather than relying on appearance alone.
How should you compare length?
Check whether the listed length includes the head. The Biaungdo listing explicitly says its 2-inch length includes the head. For other products, consult the seller’s dimensional information if the measurement is not clear. Also confirm that the screw’s usable threaded length suits the materials being joined.
Is a kit or single-size pack better?
Choose an assortment if you regularly handle varied repairs and want multiple sizes, nuts, or washers available. A single-size pack is more direct when you already know the required specification. Larger assortments provide more options but still may not include the exact thread or length your project needs.
Which material should you consider?
The listed choices include stainless steel, alloy steel, and carbon steel. Stainless steel products are described as corrosion-resistant, while the carbon steel pack is described as black. Select based on the project’s environment and appearance needs, and verify material details when they are important to the application.
Frequently Asked Questions
What is a flat head hex bolt?
It is a fastener with a flat-style head and a hexagonal socket drive. These products are commonly selected when the head profile and tool access suit the assembly.
Are metric and 1/4-20 bolts interchangeable?
No. Metric and inch fasteners use different sizing systems and thread specifications. Use the size required by the mating hole or nut.
Does screw length always exclude the head?
No. Length measurement can vary by product and head style. Check the individual listing; the Biaungdo product states that its 2-inch length includes the head.
Should I buy an assortment or a 20-piece pack?
Choose an assortment for multiple sizes and project flexibility. Choose a fixed-size pack when you have confirmed the exact diameter, thread, and length needed.