40 mm or 35 mm Forstner hinge hole
Updated: 2026-10-23
The bit says 40 mm, and the title said hinge. The concealed cabinet hinge on the bench is almost certainly a 35 mm cup. A 40 mm Forstner bit can only drill 40 mm. What to check on a general listing is on the [40 mm Forstner bit buying guide](/hub/drilling-and-accessories/forstner-bit-40mm/sub/forstner-bit-40mm-buying-guide). The product table is the [40 mm Forstner bit comparison](/hub/drilling-and-accessories/forstner-bit-40mm). Blum's cup figures and a UK cabinet guide were used below, on 20 October 2026. This is not a lab test.
The bit says 40 mm, and the title said hinge. The concealed cabinet hinge on the bench is almost certainly a 35 mm cup. A 40 mm Forstner bit can only drill 40 mm.
The bit says 40 mm, and the title said hinge. The concealed cabinet hinge on the bench is almost certainly a 35 mm cup. A 40 mm Forstner bit can only drill 40 mm. What to check on a general listing is on the 40 mm Forstner bit buying guide. The product table is the 40 mm Forstner bit comparison. Blum's cup figures and a UK cabinet guide were used below, on 20 October 2026. This is not a lab test.
Our top picks
| Badge | Product | Listed diameter | Pieces | Machine note | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  TA-VIGOR TA-VIGOR 40 mm, carbide tip | 40 mm | 1 | Bench drill, vertical drill or CNC; water on hardwood | 7.0 | about £9.46 | View offer |
 ASNOMY ASNOMY 40 mm, carbide tipped | 40 mm (minimum bore printed as 1.56 inches) | 1 | Above 40 mm, listing prefers a fixed drill or a vice | 8.5 | about £11.89 | View offer | |
| Alternative |  YOKOCUT YOKOCUT 6-piece set, 30–60 mm | 30–60 mm, including 40 mm | 6 | Drill press; reviews say larger bits walk in a hand drill | 6.6 | about £18.72 | View offer |
On this page
The cup is 35 mm unless the drawing says otherwise
Blum's Clip top Blumotion hinge 71B3550 is a 35 mm cup, about 13 mm deep, with screw centres of 45 mm. Furnica treats 35 mm as the standard cup and 26 mm for some light doors. Measure a no-name hinge. Do not trust the word hinge on an amazon.co.uk title. HSAWBIT, OUZHOU, TA-VIGOR, FBBEVWBK and ASNOMY all use hinge language beside a 40 mm cutter. The cup will drop into that hole, and the screws will miss the boring pattern.
The C-dimension
The C-dimension is the gap from the door edge to the cup edge, often about 3–7 mm. The centre of a 35 mm hole sits at C plus 17.5 mm. A 40 mm bit uses 20 mm, so the same mark is in the wrong place. Speed for a general 40 mm bit is on the how to use a Forstner bit page. Furnica's 1,000–1,500 rpm note is for the 35 mm cup only.
Depth and the centre point
The cup wants about 11.5–13 mm, matching Blum's about 13 mm. In a 16 mm door that leaves about 3 mm, and a long centre point can mark the face. A UK Workshop thread makes that the case for a shallow hinge cutter. Trend's Snappy 35 mm bit is sold with a stop from 9 mm to 13 mm, for MDF and laminated chipboard. A collar at 12 mm copies the idea. Test on scrap. The only row here with a 35 mm cutter is the YOKOCUT set at £18.72. Reviews mention blunt MDF and bits that walked in a hand drill.
When 40 mm is actually the hole
Keep the 40 mm bit when the drawing says 40 mm, for a grommet, a lock body or a pocket. Do not pack a hinge into that hole. The 45 mm screw centres miss a hole centred on a 20 mm radius, and the overlay changes. For a run of doors, or a fire door, leave the cups to someone working to the hinge maker's positions. For one kitchen door in MDF, use a 35 mm bit, a stop at about 12 mm, and a clamped stile.
Common questions
What diameter is a concealed cabinet hinge?
The usual cup is 35 mm. Blum's 71B3550 is specified as a 35 mm cup, about 13 mm deep, with 45 mm screw centres. Some light doors use a 26 mm cup. A 40 mm Forstner bit does not drill either of those. Measure the hinge you are fitting. Use 40 mm only when that measurement, or the drawing, says 40 mm.
How deep is the cup?
About 11.5–13 mm for a standard 35 mm cup, and about 13 mm on the Blum 71B3550. In a 16 mm door that leaves roughly 3 mm of timber under the cup. Set a stop and test on scrap. A centre point that is longer than the remaining thickness can mark or break the face even when the rim depth looks right.
Can a 40 mm Forstner bit drill a 35 mm cup?
No. The rim cuts the diameter it is ground to. You cannot hold a 40 mm bit inside a 35 mm circle. Listings that say hinge and 40 mm are still 40 mm holes. If the hinge in your hand is 35 mm, you need a 35 mm cutter. The YOKOCUT set in this comparison is the row that includes one, alongside the 40 mm piece.
What is the C-dimension?
It is the gap from the edge of the door to the edge of the cup, often about 3–7 mm on a standard overlay hinge. The centre of a 35 mm hole sits at that C distance plus 17.5 mm. A 40 mm bit uses a 20 mm radius, so the same mark puts the hole in the wrong place. Read C from the hinge instructions, then add half the real cup diameter.
Will the centre point come through a 16 mm door?
It can. A 13 mm cup in a 16 mm door leaves about 3 mm, and a long Forstner point will reach the face. UK workshop discussion of 35 mm bits makes that the reason some fitters prefer a shallow hinge cutter. Use a depth stop, and check an offcut of the same door before you bore the stile you will see.
Is a hinge boring bit different from a Forstner bit?
Yes, in depth and sometimes in the length of the centre. A hinge boring bit is ground for a shallow 35 mm cup, and some, such as the Trend Snappy 35 mm, include a stop around 9–13 mm for MDF and laminated chipboard. A general Forstner is happy to keep cutting deeper, which is useful for a pocket and risky on a thin door. The names overlap on cheap listings. The diameter on the shank is the fact that matters.
Related pages
Sources
Public UK sources from the research digest, last checked on 20 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the product display for this comparison.
- HSE: PPE overview (retrieved 20 October 2026)
- Consumer Rights Act 2015, section 19 (retrieved 20 October 2026)
- Bosch Professional UK, 40 mm Forstner bit 2 608 577 019 (retrieved 20 October 2026)
- Hart Wholesale, Blum 71B3550 (retrieved 20 October 2026)
- Furnica, 35 mm hinge cup guide (retrieved 20 October 2026)
- Katz-Moses Tools, Forstner speeds (US shop, rule of thumb) (retrieved 20 October 2026)
- Famag Tool UK, classic 40 mm Forstner bit (retrieved 20 October 2026)
- amazon.co.uk listings for the ASINs in this comparison (retrieved 20 October 2026)