Are you going to build a bobber or a chopper or are you going to build a custom made oil tank, then you are going to need these tabs.
These mounting tabs "Heavy Duty" can be used to put the oil tank to your frame with a rubber mount.
These tabs should be welded to the frame. The tank can then be secured with M8 or 5/16 bolts.
Of course, there are an infinite number of things you can mount on your frame. This tab is also ideal for making sissy bars.