2 truck upfitters 12" gas props (12.2" ext, 7.5" comp, 40 lbs ea) for are snugtop leer camper doors & only aluminum weatherguard only toolboxes. measurement req'd! incl 4 ball mounts! truck upfitters truck upfitters premium gas struts for camper shell rear doors. fits are, snuptop, leer, atc, & century brands, along with many others. these do not fit every camper shell brand & model door, so please measure your struts before replacing with these. these are 40 lb gas lift springs for medium weight rear or side camper doors. see our other sizes & pressures by visiting our amazon truck upfitters store.</br>installation instructions:</br>1. all gas props cannot be compressed by hand, so please do not think they are defective because the won't close using hand/arm pressure. a lot of pressure is required to compress these props!</br>2. all gas props need to be installed in the open / extended position, so please do not try to compress and install them in the compressed position. therefore, open your door to ensure your mounted props are extended.</br>3. very important: use another person's help (or 2 people for heavier doors) to hold the door in the extended position while you remove the old gas prop. do not use a broomstick or any other device to hold the door open while you remove the prop. it may fall & cause you or your vehicle serious damage.</br>4.to remove your old gas prop, use a small screwdriver to lift up on the retaining band, then pull the gas prop end away from the mount. you do not need to remove the retaining metal band, just lift it away from the nylon head enough to allow the head to come off.</br>5. to install, place the gas prop so that the wide (black part) of the gas prop (the body) is on the top, and the shaft (silver part) is on the bottom when the door is in the closed/resting position. this is so that the oil in the body will keep the seal wet, preventing it from cracking & allowing all of the pre-charged air out, resulting in failure. after aligning properly, press the nylon end head of each shock onto the 10mm ball mount. you will not need to lift up on the band to install.