The High Pressure Mill Control Packer is designed for use with Series 150 Overshots and has been successfully field tested and proven to 4,700 psi. The unique design utilizes a steel retainer ring, which can be easily installed and removed with an adjustable spanner wrench, to com­press the inner seal. The steel retainer ring is also machined with left-hand threads to prevent back-off. The body of the Mill Control Packer and the steel retainer ring are machined with a series of grooves to ensure maximum positive retention of the inner seal during high pressure operations. Correct steel retainer ring installation and proper inner seal squeeze are accurately defined when the retainer ring is flush with the top of the Mill Control Packer body.