Choosing Hex Bolts: Grade, Coating and Thread Fit
Hillman Grade 5 Zinc Plated Hex Bolts are the sensible default for general construction and repairs. Bolt Dropper 18-8 Stainless Steel Hex Bolts are the pick for anything outdoors or wet, and the Hilitchi 304 Stainless Assortment Kit is the best way to stock a workshop drawer.
For most jobs, Hillman Grade 5 Zinc Plated Hex Bolts are the right answer, with Bolt Dropper 18-8 Stainless handling corrosion prone work and the Hilitchi 304 assortment covering the odd sizes a project throws up.
Choosing bolts is genuinely confusing because a stainless bolt looks stronger than a plain steel one and is usually weaker, while a grade 8 bolt that resists enormous tension can also snap without warning if it corrodes. We compared published grade markings, tensile ratings, coatings, thread pitches and assortment contents, then weighed those against what owners report about thread quality, plating consistency and how well kits match their labelled counts.
How to choose
Grade markings tell you what the bolt can take SAE grades are stamped into the head as radial lines: no lines means grade 2, three lines means grade 5 and six lines means grade 8, with tensile strength rising accordingly. Metric bolts use numbers such as 8.8, 10.9 and 12.9 stamped on the head instead. If a repair manual specifies a grade, matching it matters, because a weaker bolt can fail under load and a harder one can be more brittle under shock.
Stainless is about corrosion, not strength This trips people up constantly. 18-8 and 304 stainless resist rust far better than plated carbon steel, but they carry a lower tensile rating than grade 5, let alone grade 8. Use stainless where moisture is the enemy, such as decks, boats, garden structures and plumbing brackets, and use graded carbon steel where the load is the enemy. Never substitute stainless into a suspension or towing application that specifies grade 8.
Match thread pitch and check for galling Coarse and fine threads are not interchangeable, and forcing the wrong pitch destroys both bolt and nut. Run a nut down by hand before reaching for a wrench, since resistance early means the pitch or the threads are wrong. Stainless on stainless is particularly prone to galling, where the threads cold weld under friction, so a dab of anti seize compound is a cheap insurance policy.
Buy assortments for variety and single sizes for projects A compartmented kit is invaluable for repairs, where the size you need is unpredictable. It is a poor way to supply a project, because you will exhaust one size and be left with dozens of the wrong ones. The practical approach is to keep an assortment in the drawer for surprises and order a bulk box of the specific size when you know what a build requires.
The shortlist, ranked
Hillman Grade 5 Zinc Plated Hex Bolts
Grade 5 medium carbon steel is the workhorse fastener for framing, machinery brackets and general repairs, and Hillman’s plating quality is consistent enough that threads run smoothly out of the box. The three radial line head marking makes grade identification easy years later. Owners report the zinc coating handles indoor and sheltered outdoor use well, though it is not a marine solution.
Pros
- Strong enough for most structural and machinery work
- Clear head markings for later identification
- Widely stocked in a broad size range
Cons
- Zinc plating corrodes in marine or salted conditions
- Not suitable where high tensile grade 8 is specified
Bolt Dropper 18-8 Stainless Steel Hex Bolts
18-8 stainless, commonly sold as 304, resists rust in rain, splash and general outdoor exposure far better than plated carbon steel. Bolt Dropper’s threads are cleanly rolled, which matters because stainless galls easily when threads are rough. Owners report using anti seize on stainless nut and bolt pairs is close to essential to avoid seizing during assembly.
Pros
- Excellent corrosion resistance for outdoor projects
- Clean thread finish reduces cross threading
- No plating to chip or wear away
Cons
- Lower tensile strength than grade 5 or 8 steel
- Prone to galling without anti seize
Hilitchi 304 Stainless Steel Hex Head Bolt Assortment Kit
This kit puts a spread of metric 304 stainless hex bolts with matching nuts and washers into a compartmented case, which is exactly what stops a small repair becoming a hardware store trip. The organisation is the real product here. Owners report the counts of the most useful mid range sizes run out fastest, so plan to top those up separately.
Pros
- Covers a wide range of sizes in one purchase
- Includes matching nuts and washers
- Case keeps sizes separated and labelled
Cons
- Popular sizes run out well before the rest
- Metric only, so no imperial coverage
Fastenere Grade 8 Yellow Zinc Hex Bolts
Grade 8 alloy steel carries a much higher tensile rating than grade 5 and is what suspension, towing and heavy machinery applications typically specify. The yellow zinc finish makes them easy to distinguish in a bin. Owners report they are noticeably harder to drill or cut, which is a feature during use and a nuisance during modification.
Pros
- Highest tensile rating of the group
- Distinctive finish and clear head markings
- Suited to towing and suspension applications
Cons
- More brittle than grade 5 under shock loads
- Coating still corrodes in salt exposure
Sutemribor Hex Head Screw Bolt and Nut Assortment Kit
Sutemribor’s kit leans toward the smaller metric diameters that appliance repairs, furniture assembly and machine work actually consume. Nuts and washers are included in matching quantities, which many cheaper kits skip. Owners report the case latches are the weak point, so transferring the contents to a better organiser is a common move.
Pros
- Strong coverage of small repair sizes
- Matching nut and washer counts
- Good value for the piece count
Cons
- Case latches are flimsy
- Little coverage of larger diameters
Glarks Hex Head Bolt and Nut Assortment Set
Glarks offers one of the highest piece counts for the money, spreading across several diameters and lengths in stainless. It suits a general household or garage drawer where variety matters more than depth in any one size. Owners report quality is fine for light duty work and that critical structural fasteners should still be bought individually to a known grade.
Pros
- Very high piece count for the price
- Broad spread of diameters and lengths
- Stainless throughout for outdoor use
Cons
- Shallow quantities in each individual size
- Not intended for structural or load rated work
uxcell M8 Stainless Steel Hex Head Bolts
When a project needs twenty of the same bolt, buying a single size in bulk beats picking a kit apart, and uxcell sells common metric diameters that way. The stainless construction handles outdoor exposure without plating concerns. Owners report thread quality is acceptable rather than excellent, so run a nut down each bolt before installation day.
Pros
- Cost effective when one size is needed in quantity
- Stainless suits outdoor installations
- Multiple lengths available in the same diameter
Cons
- Thread finish is variable between pieces
- No nuts or washers included
The lineup, side by side
| # | Model | Grade | Best for | Score | Price |
|---|---|---|---|---|---|
| 1 | Hillman Grade 5 Zinc Plated Hex Bolts | SAE Grade 5, three radial line marking | Best overall | 9.4 | Check price |
| 2 | Bolt Dropper 18-8 Stainless Steel Hex Bolts | 18-8 stainless, equivalent to 304 | Best for outdoor and wet use | 9.2 | Check price |
| 3 | Hilitchi 304 Stainless Steel Hex Head Bolt Assortment Kit | 304 stainless steel | Best assortment | 9.0 | Check price |
| 4 | Fastenere Grade 8 Yellow Zinc Hex Bolts | SAE Grade 8, six radial line marking | Best for high tension loads | 8.8 | Check price |
| 5 | Sutemribor Hex Head Screw Bolt and Nut Assortment Kit | Stainless steel | Best for small repairs | 8.5 | Check price |
| 6 | Glarks Hex Head Bolt and Nut Assortment Set | 304 stainless steel | Best value assortment | 8.3 | Check price |
| 7 | uxcell M8 Stainless Steel Hex Head Bolts | Stainless steel | Best for bulk single size | 8.0 | Check price |
Good to know
What is the difference between grade 5 and grade 8 bolts?
Grade 8 uses alloy steel with a higher tensile rating, around 150,000 psi versus roughly 120,000 for grade 5. Grade 8 is also less ductile, so it is stronger in tension but can be more brittle under sudden shock loading.
Are stainless steel bolts stronger than regular steel?
Generally no. 18-8 stainless typically has a lower tensile strength than grade 5 carbon steel. Stainless is chosen for corrosion resistance, not load capacity.
How do I identify a bolt grade?
Look at the head. Radial lines indicate SAE grade for imperial bolts, and a stamped number such as 8.8 or 10.9 indicates the property class on metric bolts. Unmarked heads generally mean low grade fasteners.
What is galling and how do I prevent it?
Galling is when stainless threads seize together under friction during tightening, sometimes permanently. Apply anti seize compound, tighten at a moderate speed rather than with a fast impact driver, and avoid dirty threads.
Can I use a hex bolt where a lag screw is specified?
Not directly. Lag screws thread into wood, while hex bolts pass through and take a nut on the far side. A through bolt is generally stronger if you can access both sides.
Should I use a lock washer or a nylon insert nut?
Nylon insert nuts resist vibration loosening well and are reusable a limited number of times. Split lock washers are cheaper and widely used, though their effectiveness is debated. Thread locking compound is another option for permanent assemblies.
Do zinc plated bolts rust?
Eventually. Zinc plating is a sacrificial layer that protects the steel for a long time indoors or in sheltered outdoor use, but salt spray, road salt and constant wetting will wear through it. Hot dip galvanised or stainless is the answer for harsh exposure.
How tight should I torque a hex bolt?
Follow the torque specification for the application and grade if one exists, since over tightening stretches the bolt beyond its yield point. Where no spec exists, published torque charts by diameter and grade are a reasonable starting point.
The verdict
Hillman Grade 5 Zinc Plated Hex Bolts cover the widest range of ordinary jobs with a known grade marking and consistent plating, which is exactly what you want from a default fastener. Move to Bolt Dropper 18-8 Stainless when moisture is the main threat, and step up to Fastenere Grade 8 only when a specification calls for it. Keep an assortment kit in the drawer for repairs, and buy single sizes in bulk when a project has a known bill of materials.
