If you are replacing casters that have been working on your chairs or furniture simply measure the attaching device ( stem or plate ) using the methods shown on our website. But if you are building a project or thinking about putting casters on a chair or furniture that currently does not have casters, be careful. A caster is a wonderful invention. It allows you to move things very easily but it relies on one geometric principle. It MUST be installed "perpendicular" to the floor. That means it has to be on a right angle to the floor. Why? So it can rotate in a circle around its attachment. If it is mounted on any angle, it will be forced into one position and it will NEVER swivel. Look at the photos shown. One chair would be a good candidate for casters and the other would not. One chair has straight legs and the other has legs that come down on an angle. You could probably install casters on the straight legged chair but never on the curved or angled leg chair. So how can you check the angel? You can use a "square" or if you don't have a square, use a cereal box or any other box in the kitchen. If the legs are straight, they will be parallel with the edges of the box and if they are not parallel on all sides, don't try to put casters on the chair.
Here is another tip. If your current casters do not swivel well, check to see if they are perpendicular to the floor. Make sure that the chair legs have not bent or maybe a socket is defective and now the caster is on an angle which would make swiveling difficult. Don't assume that you have a defective caster as it might be a bad socket or a bent leg and even if you replace the caster, you will still have the same issue.
Here are the 2 images. The 1st one could be a good candidate for casters as the legs are large and perpendicular to the floor. Casters could be installed by removing the glides on the bottom of each leg and drilling a "straight" hole into the leg to install a socket. The size and type of socket would depend on the thickness of the leg and/or the type of stem to be used on your caster.
This 2nd photo shows chairs that should not have casters installed. If you look closely, the front legs seem to be straight and perpendicular to the floor. However, the rear legs are curved backwards and are not perpendicular to the floor. This chair would NOT be a good candidate for casters.
For more information on how to choose the right caster or replacement caster, go to our short course on how to proceed. http://www.needcasters.com/how-to-measure-for-new-casters.htm