Subtle machining on the tool. The rear seal on the piston is a captive O-ring that does not seal well. So you lose some coolant when you pull on the valve core. The tool end of the piston is held and securely fastened by a roll pin. The replacement caps are made of real brass and are well made. Replacement valves are of acceptable quality. For the price, this is good value for money. But keep in mind that the price matches the quality. If you need a tool to get the job done quickly, this is a good option. But if you're a pro, this probably won't suit your needs.
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