Are you about to replace an older doorknocker with a new one? Perhaps you are looking for a different style or finish. In any case shopping for a door knocker can be a frustrating task. There is not only the choice of style and finish, you must match or cover the impressions and holes left from the previous one.
In many instances the hardest part of replacing a door knocker is finding a suitable replacement. Matching the finish or style is not so difficult as is matching the mounting methods.
There are two common methods of installing a door knocker. Surface mounting and through the door mounting. Both methods use common household tools. Other than that they are distinctly different.
First is the surface mount method. This option uses wood screws that pass through the door knocker and into the door. This is the easiest method for replacement. The screws do not have to line up perfectly with the existing holes in the door. The door knocker itself will cover the existing holes. New ones can be made without distracting from the appearance of the door. The old holes should be filled with putty in to prevent moisture from getting into the door.
Second is the through the door method. This method uses mounting hardware that passes through holes in the door to secure it from the inside. This one presents more challenges when it comes to replacement. The most obvious is the matching of the holes drilled through your door to the new door knocker. The holes need to match and be large enough to handle the hardware for the new knocker. The holes being small due to smaller diameter mounting hardware is easily fixed with a drill. If the holes are to far apart or to close this is another matter.
The distance between the holes is called the Bolt Center or BC dimension. There is a reason for this seemingly odd name. You want the bolt to go through the center of the hole so this is the point that you would mark the door to be drilled.
The problem you run into when replacing an existing door knocker is the holes are already drilled through your door. On the outside the holes can be covered by the knocker itself but on the inside they are exposed.
It can be difficult to find a new door knocker with the same BC dimension. Especially if the original one has been there for many years. There is no standard for the BC dimension. The BC for the most part is determined by the design of the knocker. The mounting lugs used to attach the hardware are usually placed at a thicker portion of the casting. This is to give them more strength.
Sometimes you have to settle for a replacement that is close. If the two BC’s are within 1/4 or 3/8 inch of each other you can usually enlarge the holes in the door a bit to make the fit. If you are lucky the existing mounting hardware will cover the enlarged holes. If not a larger washer will usually do the trick.
If the replacement door knocker BC dimension is not even close one of the existing holes can be used but the second matching hole must be drilled through the door for the mounting. This leaves the other previous hole to cover up. If puttying and repainting is not an option I have used a third mounting hardware bolt and epoxy it into the unused hole. This gives the appearance on the inside that three bolts are used on this door knocker. This looks natural and is easy to do. The outside portion of the hole is covered by the door knocker but should still be filled with putty to prevent future problems with moisture.
With a little luck you will find a matching door knocker. Be aware that this very often is not the case. Remember that if your door knocker is solid brass is may be easier to simply refinish the existing one.