If you measure from the end of the extrusion to the closest end of the feather keys, it's 223mm on the front and 189mm on the rear. If you measure from the end of the extrusion to the distant end of the feather keys (more accurate), it's 258mm on the front and 225mm on the rear. The length of the feather keys is far less than precise, so it's best to measure from the end of the extrusion to the distant end of the feather keys where they meet with the front and rear brackets. Be prepared to adopt a system of squaring the fence to the rail. There are many methods to choose from.