Mini clock inserts are popular accessories for scroll saw projects. They are relatively inexpensive, easy to install and make nice little gifts. They range in price from $5 to $15 for the insert. There are many different styles of face plate so you can find one that matches the pattern you have.
They also range in quality. It can be difficult to determine the quality of the insert from the online advertisement. Usually the less expensive inserts will be categorized as "Economy Inserts". This does not always hold true so read the ad closely then ask questions of other more experienced scrollers. The common difference in quality is a metal bezel and glass face cover vs plastic. I find that even the economy models are fine for most scroll saw projects.
In the image above you will see the backs of two different mounting styles. All the inserts fit in a hole drilled in the wood at a certain diameter and depth. The insert on the left is secured in the hole with small clips. The clips apply pressure to the inside of the hole. These are called "friction fit" inserts. The image on the right shows a "rubber ring" insert. The rubber ring wraps around the insert and when pressed into the hole makes a tight fit. I have used both types and prefer the friction fit but honestly I usually just buy the best price available at the time.
The best method to drill the hole for the insert is to use a forstner bit. (pictured above) Each size insert requires a different size bit. The most common inserts used are the 1 7/16" (36mm). These inserts require a 1 3/8" hole. You can buy the forstner bits individually or in sets. The insert will have specifications for the depth required. You can find them at most hardware and woodworking stores. Many of the retailers who sell the inserts also carry the forstner bit.
The links below are just a few of the places online you can find the clock inserts. I think I have purchased from all of these merchants over the years. I have not had any problems with any of them but if you read the online forums you will hear stories of poor service occasionally. Visit the sites, read the online forums and use your own judgement as to which you prefer. I am not recommending any of these merchants.
Wooden Teddy Bear
Penn State Industries
If you have never used the mini clock inserts give them a try the next time you need to give a small gift. There are hundreds of patterns available for just about any occasion.