Depending on the size of the hardware being used these holes may be up to 3/8 inch in diameter. There are things to think about on both sides of the door before you drill.

Once their exact location is determined the holes must be drilled squarely through the door. The door knocker will lie flat on the outside surface of the door. The mounting lugs are machined into the back of the door knocker so that the hardware must enter at a perpendicular angle. If the holes through the door are not square the hardware will not screw into the door knocker casting.

It is a good practice to have the finished holes large enough so that the mounting hardware fits loosely into them. A very tight fit may do well on the day that the installation is made but if your climate is like ours, there is as much as a 100 degree temperature difference from summer to winter. Changes in temperature causes expansion and contraction. This could cause damage to your door or your door knocker over time if the fit is too tight.

The actual drilling of the holes can damage the door. It is a good practice to first drill holes at the precise mounting locations that are less than half to size of the finished hole. The smaller hole would be drilled all the way through the door. This smaller hole gives you the chance to check your work as well as provides a guide for the finished holes.

With the smaller holes drilled through the door at the exact mounting locations you can drill the finished larger holes. Do not drill the finished holes all the way through. This would have the potential of damaging the surface of the door where the drill exits.

Instead, drill the hole half way from one side and then drill the rest out from the other side of the door. This will provide clean entrance points on both sides of the door.

With a little planning and careful work your door knocker installation will be a pleasing addition to your home for years to come.

A replacement door knocker installation that is a through the door mounting method, the bolt center dimension has added meaning. You will probably want to use the same drilled holes that are already in the door. If so you will have to find a new door knocker with the same bolt center dimension as the previous one.

The bolt center dimension is the measurement from the center of one bolt hole to the center of the other bolt hole. We have shown this dimension on our door knocker comparison page.

The new door knocker must match the old door knocker at this dimension or your new door knocker will not fit the existing holes.

There are no industry standards regarding the bolt center dimension or the size hardware to be used. These are left to the manufacturers discretion. They are usually dependent on the shape and style of the door knocker itself.

At times it can be difficult to find an exact match. Sometimes you have to settle for getting your replacement door knocker as close as you can to the original. Then you may make an adjustment by enlarging the holes in the door or drilling an new hole and using one of the old ones. In these cases something needs to be done with the inside of the door to cover up the old  or enlarged holes.

If the holes are enlarged they may be covered by using larger washers on the inside to cover the larger hole. If a third hole was needed the old one will need to be filled in.

The best bet is to find a replacement door knocker with the same bolt center dimension as the original one if possible.

The phrase Bolt Center references the geometric center of the diameter of the hole that is drilled for a bolt to pass through. Theoretically the center of the bolt will pass through the center of the hole as it goes through the door. In the case of our door knockers this would be the mounting bolts for the through the door mounting.

We refer to this point as the bolt center because this is the exact point that the workman should drill the hole for the bolt so it matches the door knocker. Right in the center.

In the case of our door knockers the bolt center dimension is the same as the distance between the bolts. If you measured from the bottom of one bolt to the bottom of the other the distance would be equal the bolt center dimension. This is true because both holes being drilled are the same size.

Lets imagine for an example that the top hole does not use a bolt. Instead the top hole is an eye viewer that requires a hole 3/4 inch in diameter and the bottom hole is a standard mounting bolt that needs a 3/8 inch diameter hole. In this case you could not drill holes based on the bottom of each. You would need to know where the center of each hole is and drill there.

This is why we use the term bolt center for our through the door mounting instructions.

This method works best on wooden doors although it can be used on metal and filled doors. The screws supplied with our Your-Door-Knocker.com door knockers are #6 wood screws. They are made of brass and finished to match the door knocker. These screws will not work well or at all on metal or filled doors without a little help.

If using a surface mount on metal or filled doors, plastic anchors available in most hardware stores should be used. A plastic anchor will give the wood screw something to thread into. A wood screw does not have the same threads as a metal screw so it simply will not grip into the metal. The metal used to make the door is probably harder than the brass. The brass screw will in all likelihood break off if you try to force it into a metal door without using an anchor.

Most filled doors have a relatively thin plastic or acrylic skin. While you may be able to get the screw to thread into this material, it will not hold the screw securely. Over time the screws will loose their grip and become loose without an anchor.

Plastic anchors are not supplied with our door knockers. They will need to be purchased if needed. Our surface mount door knockers use #6 size screws. Anchors will need match this size for a proper fit.

The plastic anchor is a very simple device and easy to use. The packaging it came in should tell you the size hole to drill in the door. The plastic anchor is then inserted into the hole and the screw for the door knocker screwed into the anchor. The plastic will accept the treads of the screw. As an added benefit the anchor stretches out on the inside of the door as the screw is passing through it. This makes a solid mounting to the door.

You can find more information on door knocker surface mount on the installation page of our site.