![](https://www.skipharrison.com/wp-content/uploads/2020/07/IMG_2492-2-768x1024.jpg)
The miter spline jig holds boxes and the like in place while cutting the slot for later insertion of the spline. miters joints are notoriously weak joints and a spline will greatly enhance its strength.
This jig was presented on King’s Fine Woodworking as a video and I bought the plans from their website.
![](https://www.skipharrison.com/wp-content/uploads/2020/07/IMG_2491-2-1024x634.jpg)