MIL-PRF and MIL-DTL -117H can be very confusing. MIL-PRF describes the performance standard and MIL-DTL-117H describes the packaging method. MIL-PRF is followed by additional codes such as MIL-PRF-131K, MIL-PRF-121G, MIL-PRF-22191-E, and MIL-PRF-81705-E. Each of these codes also corresponds to a packaging method. For instance MIL-PRF-131K Class 1 corresponds to MIL-DTL-117H-Type I-Class E-Style 1. These codes refer to such information as heavy duty, water/vaporproof, greaseproof, etc.