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Barrel bolt or mortice bolt

Updated: October 2026

You are about to screw a surface bolt onto a back door, or onto one leaf of a pair, because it is the cheapest extra fastening on the page. Barrel bolt or mortice bolt is the fork that decides whether that is enough. A barrel or slide bolt is a face-fixed shoot. A mortice rack bolt is buried in the door edge. A flush bolt is recessed into the inactive leaf. None of the twelve listings on the [door bolt comparison](/hub/door-and-window-security/door-bolt) is a rack bolt or a flush bolt. Peter F. compared those amazon.co.uk surface bolts with public UK guidance, updated October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You are about to screw a surface bolt onto a back door, or onto one leaf of a pair, because it is the cheapest extra fastening on the page. Barrel bolt or mortice bolt is the fork that decides whether that is enough.

Our top picks

SAYAYO SAYAYO padlock-hole slide bolt

Best overall

SAYAYO SAYAYO padlock-hole slide bolt
9.2/10about £8.49
View offer
JelKen JelKen 75 mm slide bolt, silver

Best value

JelKen JelKen 75 mm slide bolt, silver
9.0/10about £3.79
View offer
n/a Necked barrel bolt 75 mm, chrome

Rank 3

n/a Necked barrel bolt 75 mm, chrome
8.8/10about £4.99
View offer
On this page
  1. 1.Two different bolts
  2. 2.When the mortice bolt is the better extra
  3. 3.Pairs and French doors
  4. 4.What you cannot buy in this comparison
  5. 5.The condition on the way out

Two different bolts

A barrel bolt, or a flat slide, sits on the face. You throw it by hand into a keep. It is only as strong as the screws and the timber under them. The silver JelKen, the best value at about £3.79, is the short straight slide. The door bolt buying guide stays on that choice. A mortice rack bolt is cut into the edge. A spline key or a thumbturn drives it, so it is not a plate you can lever off the face. On a door about 44 mm or thicker a mortice bolt is generally stronger than a surface bolt, and surface bolts stick as timber moves.

When the mortice bolt is the better extra

Use a mortice bolt when the door is solid timber of about 44 mm, it already has a proper lock, and you want another point that is not a plate on the face. ProtectUK describes rack bolts about one third from the top and one third from the bottom on a 44 mm side door that already has a BS 3621 lock. On a final exit the Master Locksmiths Association prefers a knob-operated mortice bolt, because people need to get out. A surface bolt that has swollen tight overnight is a poor extra on the door you use at night. If you are not sure the door is thick enough, that is a locksmith’s measurement.
SAYAYO SAYAYO padlock-hole slide bolt

Testsieger

SAYAYO SAYAYO padlock-hole slide bolt
9.2/10about £8.49
View offer

Pairs and French doors

On a pair of doors, one leaf is usually the active door, with the lock, and the other is bolted shut. A flush bolt on that inactive leaf is recessed into the edge, typically at the top and the bottom. A face-fixed barrel is the wrong answer when the pair is the way into the house. Flush bolts are not in this ASIN set. Do not stretch the SAYAYO, the top pick, into that role. It is the outdoor bar with a padlock hole, on the shed door bolt page, not a French-door flush bolt. Fit any bolt so the person opening the leaf can reach it.

What you cannot buy in this comparison

None of the twelve listings is a mortice rack bolt, a flush bolt, or an indicator bolt with an outside release. There is no spline key in the boxes. If you need the buried bolt, you leave this set. A mortice is a hole in the edge and a risk of breaking out a thin door. If you are unsure of the thickness, stop and get it measured.

The condition on the way out

A door on an escape route should open without a key and without more than one mechanism. A slide at the top of the door fails that in practice, because leaving means hunting for a second action. A flat entrance is the BS 8621 case: a thumbturn so people can leave without a key. A fire door keeps the hardware in its test evidence. Move to a knob-operated mortice, or to flush bolts on an inactive leaf, when the door is thick timber and already has a proper lock.

Common questions

What thickness of door do I need?
About 44 mm of solid timber is the figure ProtectUK and the Master Locksmiths Association use before mortice locks and mortice bolts. These surface bolts do not need that thickness to be screwed on, and a thin door will not hold them against a shove either. If you cannot measure 44 mm of solid timber, do not start a mortice.
French doors: surface bolt or flush bolt?
Use flush bolts, or mortice bolts, at the top and bottom of the inactive leaf when the pair is a way in. A face-fixed 75 mm barrel is extra fastening for a simple leaf, not the security point on French doors. Flush bolts are not among the twelve listings here. The SAYAYO gate bar is a surface bolt with a padlock hole, not that recessed bolt.
Can I use a surface bolt at night on the back door?
Only with the escape condition in mind. The Master Locksmiths Association prefers a knob-operated mortice bolt on a final exit. A surface bolt that sticks when the door swells is a poor night-time fastening on the way out. It must not be the only way to open that door. Loose-key bolts stay off the escape route.
Does any listing here include a spline key?
No. A spline key belongs to a mortice rack bolt, and none of these twelve is that product. Attribute lines that mention a thread, a grade or Wi-Fi contradict the product text. Read the title. The necked chrome barrel is still a face-fixed shoot. If you need the key, you are in a different category.
Who fits a mortice if I am not sure of the thickness?
A locksmith or a joiner, after the door is measured. Glazing bars, a steel skin or an old mortice make the drilling uncertain. The fitting sequence in this cluster is for a surface bolt on sound timber. It is not a mortice tutorial, and this comparison cannot sell you the rack bolt. Stop before the first hole in the edge if the thickness is a guess.

Related pages

How to fit a barrel bolt

Door bolt

Best door bolt: cupboard slide, chrome or gate bar

Door bolt buying guide: type, length and the metal

Shed door bolt: padbolt, or two hasps and padlocks

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk figures on the twelve listings. No BS EN 12051 grade is claimed, because none of the listings prints the code.

  1. DHF: bolts to BS EN 12051:2000 (retrieved October 2026)
  2. Secured by Design: locks and associated hardware (retrieved October 2026)
  3. ProtectUK: security at home (retrieved October 2026)
  4. Secured by Design: secure sheds and outbuildings (retrieved October 2026)
  5. IronmongeryDirect: which type of door bolt (retrieved October 2026)
  6. The Crime Prevention Website: other door locks and bolts (retrieved October 2026)
  7. DHF: requirements for escape doors (retrieved October 2026)
  8. Master Locksmiths Association: minimum security requirements, January 2025 (retrieved October 2026)