The bulkhead spacer is designed to be used with an existing bulkhead and hardpoint provided the hardpoint is no larger than 1/4-20 and has at least 21 mm of shank length beyond the bulkhead (including existing nut.
If you have the space to add a new hardpoint for sled attachment then ideally use a 1/4-20 bolt of your choosing and two nylon locknuts (one to hold the bolt permanently to the bulkhead, and one to hold your sled to the bolt).
Secure your sled
Eggfinder sled used as example in pictures: Cut your hardpoint shank to length (21-23 mm beyond bulkhead), drop the bulkhead spacer over the shank so that the existing nut fits inside the spacer recess, and screw the sled onto the existing shank using a lock nut in the sled's nut capture.
Hook up the power, and properly secure the connector to something to support it in flight...I like to tape the JST connectors, and cable tie them to a fixed point for support, usually a battery support cable tie.