Picking the wrong tower bolt size is the most common small mistake in home hardware, and it is almost always the same one. People buy a bolt that is too short for the door because the shorter one looked neater on the shop counter. A month later the bolt is wobbling, the screws are working loose, and the door rattles every time a lorry goes past.
The fix is simple. Know what each size is meant for, measure once, and buy for the job rather than for looks.
How tower bolt sizes in inches are counted
In India, tower bolts are almost always sold by length in inches. The number refers to the length of the body, meaning the plate or barrel that screws onto the door, not the amount of bolt that slides out.
That distinction matters. A 6 inch bolt does not throw six inches into the frame. Its sliding rod is longer than the body so it can reach the keeper, but the throw itself is only a part of that length. Longer bodies generally mean a longer rod, more screw holes and a firmer grip on the door, which is why size and strength tend to go together.
Common sizes in shops run 2, 3, 4, 6, 8, 10 and 12 inch. Some ranges also include odd sizes in between, but these seven cover nearly every home.
Small sizes from 2 to 4 inch
The smallest bolts are for light, low-stress jobs.
A 2 or 3 inch bolt suits cupboard shutters, kitchen cabinet doors, small windows on a bathroom ventilator, and the inner leaf of a pair of wardrobe doors. They hold a shutter closed, nothing more. Do not expect them to keep a door shut against a push.
A 4 inch bolt is the workhorse for windows. Casement windows, balcony window shutters and lightweight internal doors such as a store room or a pantry are a good fit. It is also the size many people use at the top of a bathroom door, where the bolt is mostly there to stop the door swinging in a draught.
Medium sizes from 6 to 8 inch
This is where most interior doors live.
A 6 inch bolt is the usual choice for bedroom and bathroom doors on the inside. It has enough screw holes to sit firmly on a flush door and enough rod length to engage a keeper properly on the frame or floor.
An 8 inch bolt suits heavier internal doors, the inactive leaf of a double door, and balcony doors that face wind. On a double door, fitting an 8 inch bolt at the top and another at the bottom of the passive leaf gives the main lock something solid to close against.
Our general rule is that if a door is one you would lock at night, start at 6 inch and go up rather than down.
Large sizes and the 12 inch tower bolt
The long bolts are built for main doors, gates and anything heavy.
A 10 inch bolt suits main doors, terrace doors and the shutters of shops. It gives a long, rigid body with plenty of screws, which spreads the load across more of the door.
A 12 inch tower bolt is the one to use on heavy wooden main doors, tall double doors in bungalows, godown doors and the fixed leaf of iron gates. At this length you can usually drill a deeper hole in the floor or a stronger keeper into the frame, and the bolt can take a real push without bending. On a gate, it is common to fit one at the bottom into a floor socket and a second near the top.
Big bolts look heavy on a slim interior door, so do not overdo it. A 12 inch bolt on a bathroom door is not stronger in any useful way. It simply looks out of place.
How to measure tower bolt length for your door
Here is how to measure tower bolt length before you buy, in three quick steps.
- Check the width of the door stile or frame member where the bolt will sit. The bolt body must fit within it with a little margin on each side.
- Measure the gap from the door edge to the keeper position, whether that is the floor, the top frame or the other leaf. The rod must reach it with some extra engagement.
- Note the door material. Aluminium profiles and PVC doors usually need shorter, lighter bolts with screws suited to thin sections, while solid wood can take longer, heavier ones.
If you are replacing an old bolt, simply measure the old body end to end and match it. Reusing the same holes saves the door from extra drilling.
Finish and material, briefly
Aluminium tower bolts are light, do not rust and come in finishes such as silver satin, black, gold matt and rose gold, which makes them easy to match with handles. On a door that already has brass antique hardware, a brass-toned bolt looks more at home. Whatever you choose, keep the tower bolt finish the same as the handle on the same face of the door.
Also read
Talk to Atom Locks about sizes
Atom Locks has been making tower bolts, aldrops and other door hardware in Aligarh since 2002, including aluminium tower bolts in several finishes. You can check the sizes and finishes on www.atomlocks.com or buy from shop.atomlocks.com. If you need bolts in quantity for a building project, send the details through the Bulk Query form. For sizing questions, call +91 9412273735 or email sa***@*******ks.com.
