Abstract: In a testing apparatus used to observe the effects of positive pressure and vacuum pressure on a test specimen, such as the effects resulting from forces created by wind, explosions and water, a clamp system is provided for holding the test specimen against the apparatus in a manner which creates an airtight cavity between the test apparatus and the specimen. The clamp system includes one or more rolling clamp assemblies which are selectively movable in relation to the test apparatus in order to accommodate a range of sizes of specimens to be clamped at various locations on the test apparatus. Each clamp assembly includes an elongate track formed by spaced, parallel rails supported on a rolling trolley. One or more clamp members slidably carried on the track each include a threaded rod extending between the rails and a pivoting foot on the distal end of the rod for engaging the specimen.