Question 1

What is the difference between a Pozidriv and a Phillips screw, and does it matter?

Accepted Answer

Yes, it matters more than most people realise. Pozidriv has four additional smaller ribs between the main cross slots, giving the driver bit a much more positive engagement and dramatically reducing cam-out under power driving. Phillips heads are designed to cam out at a certain torque — useful on production lines, frustrating everywhere else. If you're driving screws with a cordless drill, always use Pozidriv or Torx where available. Attempting to drive a Pozidriv screw with a Phillips bit (or vice versa) will damage the head quickly.

Question 2

Can I use zinc-plated screws for outdoor decking or fencing?

Accepted Answer

No — zinc-plated screws will rust within one to two seasons in outdoor UK conditions and should not be used for decking or fencing. Hot-dip galvanised or stainless steel A2 are the minimum for exposed outdoor timber. If the timber is pressure-treated (which most decking and fencing timber is), the copper-based preservatives actively accelerate corrosion on standard steel; stainless A2 or A4 is strongly recommended. The cost difference per screw is small compared to the cost of replacing corroded fixings and damaged timber.

Question 3

What does the grade marking on a bolt head actually mean?

Accepted Answer

The grade indicates the bolt's tensile strength — its maximum load capacity before failure. Grade 4.6 is standard mild steel, suitable for light-duty fixings. Grade 8.8 is the workhorse of structural engineering, with roughly double the tensile strength of 4.6. Grade 10.9 is high-tensile, used where maximum clamping force in a compact size is needed. For stainless steel, A2-70 and A4-80 are the common structural grades. Never substitute a lower grade in a load-bearing application — the marking is a safety specification, not a suggestion.

Question 4

Are assortment kits actually good value, or do they just include sizes you never use?

Accepted Answer

It depends entirely on your use case. For a workshop or van stock where you encounter varied jobs, a 300–750 piece assortment kit is genuinely cost-effective — the per-unit price is far lower than buying individual packs, and having the right size to hand saves trips to the merchant. For a specific project with defined requirements, a single-size pack of 100 is usually better value and avoids leftover stock. The KS Tools 750-piece M3 assortment, for instance, is excellent for electronics and light engineering; the Draper Tools 305-piece self-tapping kit covers most general DIY scenarios well.

Question 5

What causes thread stripping, and how do I avoid it?

Accepted Answer

Thread stripping is almost always caused by over-tightening, using the wrong size fastener, or driving into a material that's too soft to hold the thread. The fix is straightforward: use a torque specification where one exists (particularly for structural bolts), pre-drill the correct pilot hole diameter for wood screws, and never force a fastener that feels tight before it's fully seated. In soft materials like MDF or chipboard, consider using a coarser thread or a larger diameter. In metal, ensure the tapped hole matches the bolt's thread pitch exactly — mixing metric and imperial threads is a common cause of immediate stripping.

Question 6

Should I use thread-locking compound or Nyloc nuts for vibration resistance?

Accepted Answer

Both work, but for different situations. Nyloc nuts (with a nylon insert) are reusable and convenient for assemblies that need occasional disassembly — they're the standard choice for most mechanical applications. Thread-locking compound (such as Loctite) is better for bolts that thread directly into tapped holes where a nut isn't practical, and is available in removable (blue) and permanent (red) grades. For high-vibration environments like engines or heavy machinery, permanent-grade compound on critical fasteners is the more reliable option. Don't use Nyloc nuts at temperatures above 120°C — the nylon insert loses its locking ability.

Question 7

Is it worth paying more for SPAX screws over cheaper alternatives?

Accepted Answer

For timber work, yes — the T-STAR plus drive and the serrated thread design genuinely perform better than generic equivalents, reducing splitting in hardwood and improving pull-out resistance. For basic metal-to-metal or general assembly work, the premium is harder to justify and a quality zinc-plated alternative from KS Tools or Draper Tools will do the job. Where SPAX earns its price is in volume timber applications: flooring, decking subframes, and structural joinery where cam-out and thread performance directly affect the quality of the finished job.

Screws & Bolts Price Comparison

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Sealey SDHX5538 screw/bolt 38 mm 100 pc(s) Screw kit

Sealey SDHX4819 screw/bolt 19 mm 100 pc(s) Screw kit

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Sealey SDHX5550 screw/bolt 50 mm 100 pc(s) Screw kit

SPAX Flat countersunk head, T-STAR plus

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Draper Tools 85531 screw/bolt 1 pc(s)

Draper Tools 85535 screw/bolt 1 pc(s)

Screws & Bolts Price Comparison