HP LaserJet 4250 Service Manual - Page 184

Screws used in the printer This table describes the screws that are used in the printer and provides guidelines to help determine where each type of screw is used. The screws can vary in length depending on the thickness of the material that is being fastened. Always note where each type of screw is located and replace each one in its original location. NOTE When you are disassembling the product, place the screws into the chassis holes from which they were removed. This prevents their loss, and ensures that the proper type and length of screw for each location is used when the product is reassembled. Table 6-1 Common fasteners used in this product Drawing and description Purpose This screw is used to fasten metal to metal when good electrical contact is needed. This screw also provides high resistance to loosening. Phillips-head machine screw with captive star washer This screw is used to fasten sheet metal or plastic to plastic frames (the deep, coarsely spaced threads provide an increased holding capability while decreasing the possibility of stripping the target hole). Phillips-head screw with self-tapping threads Reinstallation note: To install a self-tapping screw, first turn it counterclockwise to align it with the existing thread pattern, and then carefully turn it clockwise to tighten it. You will feel resistance and hear the screw click when it engages the existing threads in the hole. Do not overtighten the screw. If a self-tapping screw-hole becomes stripped, repair the screwhole or replace the affected assembly. This screw is used to fasten sheet metal parts to the sheetmetal chassis. It spans large clearance holes and distributes the load by increasing the bearing surface. Phillips washer-head machine screw with a broad, flat washer attached to the screw head Screw measurement guide 170 6 Removing and replacing parts