{"product_id":"liftmaster-71-1550b72qkh","title":"LiftMaster 71-1550B72QKH Drive Sprocket — #50, 72 Teeth, 1-1\/4-Inch Bore","description":"\u003cp\u003e\u003cstrong\u003eThe LiftMaster 71-1550B72QKH is a 72-tooth drive sprocket specified for #50 chain, with a 1-1\/4-inch bore and a 3\/8-inch keyway. The supplier also identifies two set screws. It must be selected as part of the approved operator drive ratio and shaft arrangement rather than by chain size alone. Select the replacement by the complete part number and the installed equipment configuration. A similar photograph or a shared LiftMaster brand name does not establish interchangeability. Confirm the applicable service drawing before ordering so the repair addresses the correct component and its related mounting, connection and operating requirements.\u003c\/strong\u003e\u003c\/p\u003e\u003ch2\u003eCompatibility — Models, Versions and Exclusions\u003c\/h2\u003e\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eModel or selection point\u003c\/th\u003e\n\u003cth\u003eCompatibility requirement\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eApproved sprocket selection tables\u003c\/td\u003e\n\u003ctd\u003eMatch door type, load and operator configuration.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOther #50 chain drives\u003c\/td\u003e\n\u003ctd\u003eSame chain size does not establish bore or ratio suitability.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e1-1\/4-inch shafts\u003c\/td\u003e\n\u003ctd\u003eKeyway, hub and alignment must also match.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e#41 chain systems\u003c\/td\u003e\n\u003ctd\u003eDifferent chain specification; not an interchangeable drive choice.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\u003ch2\u003eIdentify the Assembly and Plan the Repair\u003c\/h2\u003e\u003cp\u003eThe manufacturer’s MAXUM sprocket bulletin treats sprocket selection as an application decision. A different tooth count changes the drive relationship; it is not simply an alternative diameter that may be installed wherever space permits. Have the technician verify the specified combination for the actual door and operator before changing a ratio.\u003c\/p\u003e\u003cp\u003eInspect chain condition, alignment, shaft engagement and the mating key. Two set screws do not eliminate the need for the correct key and approved retention procedure. A new sprocket should not be fitted over a damaged keyway or used with worn chain simply to get the door moving again.\u003c\/p\u003e\u003cp\u003eCompare the replacement with the installed service arrangement before dismantling the equipment. Photograph the part’s location and record the complete model and visible service numbers. Inspect the surrounding attachment points and mating components for wear, impact damage or misalignment. Replacing one worn item will not correct a damaged support or another component that continues to impose abnormal loads on the repaired assembly.\u003c\/p\u003e\u003cp\u003ePlan the repair around the manufacturer’s instructions for the actual equipment revision. Confirm access, safe support and any separate hardware before removing the old part. After installation, restore the intended retention, alignment and guarding, then test the equipment under controlled conditions. The repair is complete only when the original fault has been addressed and the system’s required operating and protection functions have been checked.\u003c\/p\u003e\u003ch2\u003eSpecifications and Product Identification\u003c\/h2\u003e\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eSpecification\u003c\/th\u003e\n\u003cth\u003eDetails\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eOrdering reference\u003c\/td\u003e\n\u003ctd\u003e71-1550B72QKH\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eChain size\u003c\/td\u003e\n\u003ctd\u003e#50\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTeeth\u003c\/td\u003e\n\u003ctd\u003e72\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBore\u003c\/td\u003e\n\u003ctd\u003e1-1\/4 inches\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eKeyway\u003c\/td\u003e\n\u003ctd\u003e3\/8 inch\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSupplier retention description\u003c\/td\u003e\n\u003ctd\u003eTwo set screws\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\u003ch2\u003eBefore Ordering\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eConfirm all four dimensions: chain, teeth, bore and keyway.\u003c\/li\u003e\n\u003cli\u003eCheck the approved operator\/door sprocket combination.\u003c\/li\u003e\n\u003cli\u003eInspect the shaft, key and mating drive.\u003c\/li\u003e\n\u003cli\u003eConfirm required guards and retention hardware.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003ePackage Contents and Separate Requirements\u003c\/h2\u003e\u003cp\u003eThe listing identifies the sprocket, with two set screws in the supplier description. Do not assume that chain, a shaft key, companion sprocket, guard or complete drive assembly is included. Confirm the current package and obtain any separate components required by the approved drive configuration.\u003c\/p\u003e\u003ch2 class=\"safety-warning\"\u003eSafety Warnings — Read Before Installation or Service\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eWARNING: A moving commercial door and exposed drive sprocket — #50, 72 teeth, 1-1\/4-inch bore can cause serious injury or death. Have a trained door-systems technician perform installation and service.\u003c\/li\u003e\n\u003cli\u003eDisconnect mains power and any battery backup before mechanical work or wiring. Secure the door against unexpected movement as directed by its manufacturer.\u003c\/li\u003e\n\u003cli\u003eDo not work on springs, cables or counterbalance components without appropriate training. Never bypass safety sensors or increase force to overcome binding.\u003c\/li\u003e\n\u003cli\u003eRestore guards and complete the model-specific travel, reversal and protection-device tests before returning the door to normal operation.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eRelated Products and Important Differences\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/garage-doorparts.com\/products\/liftmaster-photocell-kit-indoor-only-for-30-wide-openings\"\u003eCPS-U monitored photo eyes\u003c\/a\u003e — separate protection devices for approved commercial-door controls; match the operator and environment.\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/garage-doorparts.com\/products\/liftmaster-extended-duty-trolley-operator\"\u003eTDC12X1BMC MAXUM trolley operator\u003c\/a\u003e — a complete-operator comparison, not evidence that this legacy service part fits MAXUM.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003ch3\u003eDoes #50 chain compatibility prove fit?\u003c\/h3\u003e\u003cp\u003eNo. Bore, keyway, hub, ratio and alignment must also agree.\u003c\/p\u003e\u003ch3\u003eWhat is the bore size?\u003c\/h3\u003e\u003cp\u003eThe documented bore is 1-1\/4 inches.\u003c\/p\u003e\u003ch3\u003eCan I select it solely by door speed?\u003c\/h3\u003e\u003cp\u003eNo. Use the approved application and drive-selection information.\u003c\/p\u003e\u003ch3\u003eIs the shaft key included?\u003c\/h3\u003e\u003cp\u003eIts inclusion is not established here; confirm the package.\u003c\/p\u003e\u003ch2\u003eNeed Help Confirming the Right Product?\u003c\/h2\u003e\u003cp\u003e\u003ca href=\"https:\/\/garage-doorparts.com\/pages\/contact\"\u003eContact Garage-DoorParts.com before ordering\u003c\/a\u003e. Send the full equipment model, readable part labels and photographs of the installed assembly. Include the dimensions, electrical configuration or accessory details relevant to your project so the listing can be checked against the actual installation.\u003c\/p\u003e","brand":"Controlled products","offers":[{"title":"Default Title","offer_id":60723627655454,"sku":"71-1550B72QKH","price":97.53,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0978\/2781\/5710\/files\/71-1550b72qkh.png?v=1793245138","url":"https:\/\/garage-doorparts.com\/products\/liftmaster-71-1550b72qkh","provider":"garage-doorparts.com","version":"1.0","type":"link"}