Our SP-004 features improved durability, surface and base compared to the SP-003. The SP-004 features a fullback base, made from high-quality 60A Silicone, capable of gripping securely to even the most slippery desk surfaces. The SP-004 also features an improved Silicate Glass surface, capable of providing more precise tracking, while being more silent than the SP-003. This surface, and the entire glass pad itself is extremely durable, due to our unique tempering process which results in matching the strength of security glass.