Even a little extra space can cause big damage
Cast iron is strong, durable and loved for its authentic look. But it’s one of the few materials you should never drill into or enlarge holes in.
It can be tempting to make an existing hole slightly bigger — for example, to use a coach screw or a thicker fixing — but with cast iron fittings such as hinges, door handles or shelf brackets, that’s a bad idea.
Why cast iron doesn’t like to be reworked
Cast iron is hard but brittle.
It contains a high amount of carbon, which gives it strength but also makes it sensitive to stress.
Unlike steel, it doesn’t bend — it cracks or breaks suddenly when pressure builds up.
When you drill out a hole, you create local heat and stress in the metal.
Even a small amount of misalignment or excessive pressure can cause microcracks or flaking.
What can happen when you drill out holes
If you try to enlarge an existing hole in cast iron:
-
The edge can crumble, especially on thin parts like hinge wings or shelf brackets.
-
The hole can distort, causing the screw or bolt to fit poorly.
-
And with the slightest mistake, the metal can break completely — suddenly and without warning.
The part then loses its strength, stability and finish.
Even when the damage isn’t visible, cracks can spread during installation.
Why larger screws aren’t the answer
Many assume that a larger screw or coach bolt will make the fitting stronger,
but cast iron parts aren’t designed for that.
The original screw holes are carefully sized to provide the right pressure distribution.
A thicker screw puts more stress on the hole edge — exactly where cast iron is weakest.
Better alternatives
If you need more support:
-
Use a longer screw instead of a thicker one;
-
Add a washer or spacer to maintain the existing fit;
-
Or mount additional brackets or hooks rather than modifying the original piece.
That way, your fitting remains strong, safe and authentic.
In summary
Drilling out holes in cast iron may seem harmless, but it weakens the material permanently.
Cast iron isn’t meant to be reworked — one wrong move, and it breaks.
If you want your door handles, hinges or shelf brackets to last, use them as designed.