If the steel rod has no block fixed to the top of it you will need to buy a double ended suspension and screw it onto the rod. If for some reason the suspension steel of a new double ended suspension is the wrong length, you will need to follow the next step to modify the length:

If you purchase a single ended suspension it can easily be fitted to most clocks that have block at the top of the rod (The suspension's bottom block). If you look at the existing bottom block you should see a pin passing through the sides. Place the block on a solid surface that has a hole in it. Make sure the pin is over the hole. If it appears to be a tapered pin, make sure the larger end is below. Using another smaller pin and a hammer, drive out the old pin. Keep the old pin!

Break off the new suspension at the desired length and place it between the two sides of the bottom block. Put the old pin (smaller end downwards) into the hole. This time using a solid surface with no hole and using a small hammer, tap the pin through the suspension spring. There is no need to make a hole beforehand because the pin will act as a punch.

It is important that a suspension spring is not tightly held between the sides of the bottom block. The clock needs to be able to operate on a floor that may cause it to lean slightly forward or back, or in a case that is warped. If the suspension is pinched tightly the steel strip may distort each time it passes the centre point.

Repairing Your Own Clocks by Mervyn Passmore