There are four bolt holes with 7/16" fine threads in the bed behind the back seat of my '69 Blazer. Anyone know what they were used for? These seem to be factory installed. They have the stamped formed plate under the bed. I was planning to weld them closed, but got curious. Did the factory offer some sort of storage box that was bolted to the floor? These are not bolt holes drilled by a previous owner. I've got evidence of his intelligence, such as, cutting away part of a support brace so that a bolt for the rollbar would fit. Any knowledge of what these four holes are?