I forget about the OHSAA pre-season manual, because I don't consider it a "rules book." But, oldthrower75 is correct. It is clearly stated on page 21 in that document.
All rules relative to safety in the field events must be strictly adhered to. In addition, in those events in which implements must be weighed and gauged or certified as legal (shot put and discus), once those implements are certified, competitors may not remove them until the competition has concluded. The use of the term “common implements” means that the games committee has determined that competitors may use only those implements provided by the competition site. In all other circumstances, competitors may provide their own implements that shall be determined to be legal as mandated by the games committee in accordance with NFHS rules. No official has the authority to compel an athlete to share his or her implement with another competitor.