Four Year HistoryInertial got its start four-and one half years ago with $100,000 capitalization and a shop in the Philadelphia Rivet Co. plant, 226 N. Broad St., D o ylestovvn. Mihalko and Schmalbruch were the only full time employes.Horace Collins, owner of Philadelphia Rivet, and Mrs. Martin Toll, wife of the former president of Chem-Fab Corp., 300 N. Broad St., helped the pair form the company.Through the Doylestown stock brokerage firm of Ren-neisen, Renneisen and Red-field, Inc., Inertial went public in February with an over-the-counter stock issue of