Each product is manufactured using strict quality control standards resulting in consistent cap dimensions with septa which may be certified for higher purity grades. All our caps and septa are packed in a clean environment to ensure you receive contaminant free product every time. PerkinElmer closures are manufactured to specific tolerances that are guaranteed to fit and perform with PerkinElmer and non-PerkinElmer instruments. I. D. : 20 mm Finish: Crimp Top Cap with Septa Description: PTFE/Silicone with Aluminum Cap (silver)