Most doors fail at the frame, not at the lock · review
A pair of concealed flush bolts in 304 stainless steel, let into the edge of the door so that nothing protrudes. Prmape states bolts 150 mm (5.91 in) long overall, a brushed finish and stainless fixings.
The conclusion The right hardware for a passive leaf, and a genuine joinery job to fit. Sleeve the receiving holes.
Double doors and French doors have a structural problem: one leaf is held by its lock, and the other is held by whatever bolts it into the frame. If those bolts are absent or shallow, the pair opens together and the lock on the active leaf was never relevant.
Concealed flush bolts, let into the edge of the passive leaf so nothing shows and nothing can be gripped. 304 stainless, so they survive an exterior door, and 150 mm (5.91 in) long overall. Prmape does not publish the bolt throw, which is how deep it drops into the head above and the threshold below.
Not the bolt. The hole it drops into. A bolt entering 8 mm (0.31 in) of soft timber holds nothing at all, and that is the usual failure. The receiving holes want to be deep, and ideally sleeved with a metal socket so the timber around them cannot crush.
The bolt is the cheap half of this job. The holes are the half that matters.
This is a mortice cut into the edge of a door: a recess exactly the size and depth of the bolt body, cut straight, plus drilled receivers top and bottom aligned to it. It is joinery. A mis-cut mortice in a door leaf is not recoverable, and if that sentence gives you pause, this is a job to hand over.
Anybody with French doors or a double door, and either the skills or the budget to have them fitted properly.
Not found on the American Amazon store, where the buy link falls back to a local search rather than to a page that does not exist.
Prices and availability are what Keepa reported on the date this page was updated; both move.
| Type | Concealed flush bolt, pair |
|---|---|
| Material | 304 stainless steel, brushed |
| Length | 150 mm (5.91 in) overall; bolt throw not published |
| Installation | Let into the edge of the door |
| Fixings | Stainless screws supplied |
| Amazon reference | B09K3RHMHS |
| EAN | 0635638989849 |
Holding the passive leaf of a double door. On French doors or a pair of doors, one leaf opens daily and the other is meant to stay shut — and unless it is bolted top and bottom into the head and the threshold, the whole pair is only as strong as a latch on the leaf that moves.
Only if you are comfortable cutting a mortice into the edge of a door. The bolt sits flush, which means a recess exactly its size and depth, plus holes drilled into the frame head and the threshold for it to drop into. It is a joinery job, and a mis-cut mortice cannot be undone.
They are the whole thing. A bolt that drops into a shallow hole in soft timber holds nothing. The receiving hole should be sleeved with a metal socket where possible, and it should be deep enough to take the bolt's full throw.
7.8/ 10
The right hardware for a passive leaf, and a genuine joinery job to fit. Sleeve the receiving holes.
A reference exists on these Amazon stores: France, Germany, Italy, Spain, United Kingdom. Listed is not the same as in stock — availability changes daily.
Details checked on September 2, 2026.
A double door or a French door, where the passive leaf must be held top and bottom.
Specifications: the manufacturer sheet for home security products and the matching Amazon product page. Prices and availability: Keepa. Every figure on this page names its source.
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≈ $115
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