This shop kit comes with 3 of the most popular sizes includeing 3", 4" and 5" boost leak testers. These are designed to be installed directly on to the turbos compressor inlet flange. This is an important tool that every turbo car or truck owner needs in their arsenal of tools. It is going to keep the turbo healthy by eliminating leaks in the boost path. It is a must if you are tuned/going to get a custom tune or you are replacing any components in the intake tract such as charge hoses, intercooler, manifold, vacuum lines, injectors…etc. Also a must if you are going to the track and want the peace of mind that everything is tight and capable of handling sustained boost without blowing any hoses off Design Features: (2) Billet 6061 Aluminum End Caps (one 3" and one 4") with 1/8" NPT threaded gauge port & fitting port (3) High quality 4-layer silicon couplers Custom Stainless Steel gauges 3" cap includes 30 PSI / 1Bar Boost Gauge and 4" cap includes 15 PSI / 0.5Bar (for safety) Most leaks will be discovered under 15psi of compressor pressure.