DeFelsko AT50TKIT 50 Mm X 50 Mm Tile Conversion Kit For PosiTest AT Adhesion Testers. DeFelsko Conversion Kits for the PosiTest AT are divided into groups for testing specific substrates. Kits work with both the Manual and Automatic PosiTector models. The 50C Kit is best for concrete surfaces and overlays, the 50T Kit is best for cementitious adhesive for tiles, the 50 Kit is best for lower bond strength finishes, and the 20 Kit is best for high-bond strength finishes on metal.