Corner clamp buying guide: type, capacity and piece count
Updated: 22 October 2026
You have 18 mm plywood cut for a drawer box, and the amazon.co.uk results for a corner clamp look the same. Some will close the joint. Others only hold the corner. This corner clamp buying guide is the checklist beside the [angle clamp comparison](/hub/hand-tools/angle-clamp): choose the type, find a millimetre capacity or treat it as missing, then count fasteners rather than plates. Peter F. read these listings on 21 October 2026. There is no lab test behind the figures, and a qualifying purchase through our links can earn a commission at no extra cost to you.
You have 18 mm plywood cut for a drawer box, and the amazon.co.uk results for a corner clamp look the same. Some will close the joint. Others only hold the corner.
You have 18 mm plywood cut for a drawer box, and the amazon.co.uk results for a corner clamp look the same. Some will close the joint. Others only hold the corner. This corner clamp buying guide is the checklist beside the angle clamp comparison: choose the type, find a millimetre capacity or treat it as missing, then count fasteners rather than plates. Peter F. read these listings on 21 October 2026. There is no lab test behind the figures, and a qualifying purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Type | Stated capacity | Pieces | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Preciva Preciva 140 mm squares, pair | Positioning square | 50 mm | 2 squares | 8.6 | about £27.99 | View offer |
 Sofofux Sofofux 4-piece single-handle clamps | Jaw clamp | 55 mm | 4 clamps | 6.1 | about £22.99 | View offer | |
| Best value |  LTDOOIT LTDOOIT 4-piece corner clamps | Jaw clamp | 77 mm | 4 clamps | 6.9 | about £9.99 | View offer |
On this page
Two tools share one search
A 90 degree clamp and a positioning square answer the same search and do different work. A single-handle jaw clamp uses a screw to pull two faces together. In this set that pattern is Sofofux (ASIN B0CW2Z845G, about £22.99) and LTDOOIT (ASIN B08FMVM5SR, about £9.99). A positioning square is an L-block and does not pull a glue line shut.
Preciva (ASIN B0CW2SVRPJ, about £27.99) and QWORK (ASIN B0BVHP6SFJ, about £18.99) are that second type. A review of the Anylot squares (ASIN B0H8YC4BTC) says they do not put pressure on the joint. The longer split is on the positioning square versus corner clamp page.
Capacity is a millimetre figure, or it is missing
Capacity means the board thickness the listing actually states. Preciva and QWORK say boards up to 50 mm. Sofofux states a 55 mm range, with a jaw 70 mm wide and 25 mm deep. LTDOOIT states 77 mm. GOEDEKE (ASIN B0GR43TKN1, about £20.99) has no specification line; one review measured a 53 mm opening. Anylot, iPalamila, XUEMUO, AOQCFS and the generic ABS kit state no jaw opening.
For 18 mm plywood, a stated 50 mm opening clears the thickness. Anylot’s highlighted 13 cm bolt is a fastener length, not an opening. If the only number is a bolt or a plate, the capacity is missing.
How many corners, and how many fasteners
ITS treats two corner clamps as enough to stop a carcass racking while you fix the remaining joints. Four is the more comfortable number when every corner of a drawer must stay put. Sofofux, LTDOOIT and GOEDEKE are sold as four jaw clamps. Preciva and QWORK are pairs, so one box holds two corners.
Count rods and nuts, not only the L-plates. Anylot, about £55.99, lists eight squares in two sizes, yet one review says the rod and knobs only assemble four clamps at a time. XUEMUO is titled as four 14 cm squares at about £39.99, while the unit-count field says two.
Claims that are not specifications
A higher price in these listings does not mean the square is 90 degrees. iPalamila’s listing claims ±0.1 degree, and three reviews are too few to treat that as proof. Reviewers of the XUEMUO four-pack reported squares at 89.6 degrees and squares that were not square.
Welding copy is not a specification. MyToolShed separates these woodworking clamps from a copper-plated welder’s clamp. LTDOOIT reviews include jaws that snapped when over-tightened, so wind only until the joint is held. If the clamp arrives not as described, section 22 of the Consumer Rights Act 2015 gives at least 30 days to reject it. Who each stronger pattern suits is on the best angle clamp page.
Common questions
What capacity do I need for 18 mm plywood?
Eighteen millimetre plywood needs a stated opening at least that large. Preciva and QWORK state boards up to 50 mm, Sofofux a 55 mm range and LTDOOIT 77 mm. A square that accepts the thickness still does not close the joint. If no millimetre capacity is stated, do not invent one from a bolt or a plate size.
Is a 13 cm bolt a jaw opening?
No. On the Anylot eight-piece positioning squares (ASIN B0H8YC4BTC, about £55.99) the details list a bolt length of 13 cm. That is the fastener, not the thickness of board the square will take, and the listing states no jaw capacity. Look for a separate line such as boards up to 50 mm. If that line is absent, treat the capacity as missing.
How many clamps do I need for a drawer box?
Two clamps are enough to stop a carcass racking while you fix the other joints, which is the figure ITS uses for a box. Four is the more comfortable number when every corner of a drawer has to stay put. A four-piece jaw set such as Sofofux or LTDOOIT matches that drawer count in one box. An eight-square kit can still assemble only four if the rods cover one size at a time.
Does a higher price mean the square is 90 degrees?
In this set a higher price buys more pieces and, on Anylot and iPalamila, a case. It does not prove the angle. iPalamila (B0H8Z6213H, about £49.99) claims ±0.1 degree on the listing, and that claim has not been checked in a lab here. The listing shows three reviews. Reviewers of the XUEMUO four-pack, about £39.99, reported 89.6 degrees and squares that were not square.
What if the listing says welding?
A welding word in the title is not a specification for arc welding. A welder’s angle clamp is a different tool, typically copper-plated so spatter does not seize the screw, which is the split MyToolShed draws. The anodised squares and plastic kits here are for woodworking. Do not weld with plastic nuts or these squares, and do not use them on glass.
Are plastic squares a reasonable first buy?
They can be a first buy for light corners if you accept a missing capacity. AOQCFS is about £12.99 and the generic ABS kit is about £9.09, and neither states a millimetre opening or had a review line in the file used here. A hard cabinet jaw is a blunt match for a small mitre, which is the job on angle clamps for picture frames.
Related pages
Sources
Public UK sources from the research digest, last checked on 22 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the display file.
- GOV.UK, General Product Safety Regulations 2005 (retrieved 22 October 2026)
- GOV.UK, product safety advice for businesses (retrieved 22 October 2026)
- Consumer Rights Act 2015, section 22 (retrieved 22 October 2026)
- HSE, PUWER overview (retrieved 22 October 2026)
- HSE, woodworking standards (retrieved 22 October 2026)
- ITS, corner clamps and angle clamps (retrieved 22 October 2026)
- MyToolShed, corner clamps (retrieved 22 October 2026)
- Fine Woodworking, tips for square glue-ups (retrieved 22 October 2026)