Captive sleeve compression fittings are for use in instrumentation and pneumatic applications. They are designed to be used with copper, aluminum, and plastic tubing. Captive Sleeve Compression Fittings Do Not Need Any Flaring, Fusing or Other Types of Tubing Preparation. Quicker to Assemble than Flare or Standard Compression Fittings. Captive Sleeve Bodies are Interchangeable with Standard Compression Fittings. Working pressure is dependant on tube contruction and thickness. They have a temperature range of -65F to 250F. From under the hood, to the back of the trailer...We've got you covered!