The Bottom Bracket Fixture is used to support the bottom bracket shell of your bicycle frame. It comes with the plates and hardware shown in the first picture and works with 2"x2" tubing only (customer-supplied). Bottom Bracket Cones are sold separately. The 7/16" bolt holes (in the 90-degree brackets) are slotted 3/16" of an inch to allow for fine adjustments if the tubing they mount to it isn't welded perfectly perpendicular to the lower rails of the frame jig.
For cruiser bicycle frames with the bottom bracket high in the frame, you may want to create a Tee from 2"x2" tubing (as shown in the last picture) and mount the fixture brackets to the top of the tee facing the rear dropouts. This will require an additional Base Clamp to support the welded Tee. You can also make a welded "L" from 2"x2" tubing and clamp it to the outside of one frame rail of the jig (with a spacer) like the upright for the seat tube fixture. The fixture brackets can then be mounted to the horizontal part of the "L".
You need to supply the tubing for the fixture. If you plan to use the fixture as shown in the third and fourth photos, the tubing is welded in the same manner as the Adjustable Width Fixture and similar to the Feet. Download the Frame Jig Plans / Assembly Instructions (these instructions are for the motorcycle frame jig, but will give you a good idea of how it all goes together as the bicycle-specific instructions are coming soon)
The steel plates for the bottom bracket fixture are powder-coated black.
You may also be interested in the following product(s)
Basic Bicycle Frame Jig Kit (Welding Jig / Fixture)
Full Bicycle Frame Jig Kit (Welding Jig / Fixture)