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Spot weld drill buying guide: shape, size, then steel

Updated: October 2026

You are about to buy a spot weld drill, and the amazon.co.uk titles sound like the same tool. Some are one solid bit, some are a crown that cuts a ring, and some are a hole-saw box with a cutter buried in the pack. This spot weld drill buying guide is the order to use before you open the [spot weld drill comparison](/hub/drilling-and-accessories/spot-weld-drill): the shape of the cut, a millimetre size you can point at, the material sentence, then how many pieces actually cut welds. Listed prices there run from about £7.48 to £16.99. That band is this shelf, not every UK trade counter. The Products Compared editorial team did not run a lab test.

You are about to buy a spot weld drill, and the amazon.co.uk titles sound like the same tool. Some are one solid bit, some are a crown that cuts a ring, and some are a hole-saw box with a cutter buried in the pack.

Our top picks

Sealey Sealey AK4734 8 mm spot weld drill

Best overall

Sealey Sealey AK4734 8 mm spot weld drill
8.6/10about £7.99
View offer
BGS BGS 1632 10-piece spot weld drill set

Alternative

BGS BGS 1632 10-piece spot weld drill set
8.0/10about £16.92
View offer
Gasea Gasea 6 mm and 8 mm spot weld bits

Best value

Gasea Gasea 6 mm and 8 mm spot weld bits
7.1/10about £7.79
View offer
On this page
  1. 1.Three products under one name
  2. 2.Diameters you can defend
  3. 3.Cobalt, coating, and piece count
  4. 4.What you still check on the comparison

Three products under one name

A solid spot-weld bit mills the nugget. Castle Brooke Tools publishes 6.0 mm by 66 mm and 8.0 mm by 79 mm in HSS with 5% cobalt. An annular crown cuts a ring and leaves a button. Laser Tools describes that pattern next to an 8 mm cobalt bit. The third product is a mixed kit whose contents are mostly hole openers or hole saws. Read the included-items line before the stars. Sealey's AK4734 page states 8 mm and 80 mm overall. That is a published size, not a rule that every flange is an 8 mm weld.

Diameters you can defend

Match the cutter to the weld, then to the flange you mean to keep. A 6 mm bit takes a smaller nugget. An 8 mm bit is the size those two UK pages print. Bohaner's listing states 6 mm by 66 mm and 8 mm by 79 mm, in line with the Castle Brooke lengths, not proof the bits are the same tool. 6.5 mm sits between 8 mm and 10 mm when an 8 mm hole would eat a slim flange. 9.5 mm on the BGS 1632 line is a crown diameter, not a third solid size. 10 mm takes the most metal from the sheet you keep. Three-eighths of an inch is 9.525 mm, so a title that pairs 10 mm with 3/8 inch has mixed two cutters. Topcloud states 3/8 inch and no millimetres.
Sealey Sealey AK4734 8 mm spot weld drill

Testsieger

Sealey Sealey AK4734 8 mm spot weld drill
8.6/10about £7.99
View offer

Cobalt, coating, and piece count

A gold flute is not a steel grade. HSS with 5% cobalt has to appear in words. Titanium-plated, or high-speed carbon steel with titanium nitride, has not said 5% cobalt. VBVOO says cobalt content and does not give a percent. If the percent is missing, leave it missing. Then count the pieces that cut welds. BGS states a 9.5 mm cutter, an 8 by 80 mm cobalt drill, five double-ended crowns, and two pilot pins. The pieces field says 1, so trust the contents line. Wjelet is one spot-weld drill, two centre drills, and ten hole openers. Gosknor's 12-piece line includes five hole saws. Only BGS states a speed, 700 to 2000 rpm. Do not copy that band onto a blank listing.

What you still check on the comparison

In this set prices run from about £7.48 to £16.99. Do not mix Sealey's £11.94 trade list with the about £7.99 amazon.co.uk price. A high-stress or high-strength line is that listing's wording, not a boron approval. While the bit is turning, wear eye protection and keep gloves out of the chuck path. The Health and Safety Executive's EIS16 sheet covers entanglement on rotating drills. A qualifying purchase can earn a commission at no extra cost to you.

Common questions

Should you buy 6 mm, 8 mm, or 10 mm?
Buy the diameter that covers the weld you can see and still leaves a flange you can join again. UK trade tables and Sealey both publish 8 mm for a cobalt body bit, and Castle Brooke also lists 6.0 mm. 10 mm removes more parent metal. 9.5 mm in this set is a BGS crown, not a third solid size.
Is a gold coating the same as 5% cobalt?
No. A gold or titanium finish is a coating, and the listing has to name it as a coating. Five percent cobalt is a steel sentence. Titanium nitride on high-speed carbon steel is not the Sealey line HSS with 5% cobalt. VBVOO mentions cobalt content without a percent, which is still not 5%. If the percent is missing, do not fill it in from the colour of the flute.
How many pieces in a 9-piece or 13-piece set are cutters?
Count the contents line, not the title. A crown kit can be one arbor, several double-ended heads, and a pin, so nine pieces are not nine drills. Wjelet's 13-piece listing is one spot-weld drill, two centre drills, and ten hole openers. Gosknor's 12-piece line includes five hole saws. If a line does not say cutter, crown, or spot-weld bit, it is not a spare for the weld you are about to drill.
Is 10 mm the same as 3/8 inch?
No. Three-eighths of an inch is 9.525 mm, so a title that pairs 10 mm with 3/8 inch has mixed two sizes. Topcloud states 3/8 inch and gives no millimetres, so you cannot relabel that kit as 9.5 mm or as 10 mm. BGS states 9.5 mm in words. Use the figure the listing prints, and treat a dual label as a clash.
Can high stress steel mean boron steel?
No. Galvanised and high-stress, or high-strength, in a listing is the wording on that listing. Boron and ultra-high-strength steels are a different repair. Sealey's carbide AK4740 carries the maker's boron sentence, and that bit is not one of these twelve. Do not promote a high-stress line into a boron approval because one Amazon surface field happens to say Boron.

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Sources

Public UK sources used for this comparison. Listing prices are from amazon.co.uk on 15 October 2026.

  1. Laser Tools — spot weld cutters and drills (retrieved 15 October 2026)
  2. Sealey AK4734 HSS cobalt spot weld drill bit 8 mm (retrieved 15 October 2026)
  3. Mig Tig Arc — 8 mm spot weld drill bit (retrieved 15 October 2026)
  4. HSE — PUWER overview (retrieved 15 October 2026)
  5. HSE EIS16 — glove entanglement (retrieved 15 October 2026)
  6. HSE — using the right type of PPE (retrieved 15 October 2026)
  7. Consumer Rights Act 2015, section 9 (retrieved 15 October 2026)
  8. GOV.UK — General Product Safety Regulations 2005, Great Britain (retrieved 15 October 2026)