Wilwood 200 9616 Wilwood Piston Thermlock 1.38in x .88in Qu es la Psicologa PsicoActiva. Wilwood 200 9616 Wilwood Piston Thermlock 1. 38in x . 88in Wilwoods exclusive Thermlock Pistons provide the most effective thermal barrier available for minimizing heat transfer from the brake pads to the caliper body, seals and fluid. This innovative multi part design incorporates a stainless steel shield and coated aluminum shell configuration that effectively retards heat transfer by at least 25 percent. This reduction in operating temperature eliminates seal crystallization and localized fluid boiling, which decreases distortion in the caliper body and piston bores, extending overall service life.