this is to help carpenters to drill the pilot holes for common door handles and lock plates. you simple slot the correct shape into the lock mech and then use the holes to drill the pilot holes. this is great for barrelled locks because you use the level thats built in. the device is designed to have 4 brass inserts that can be purchased very cheap on amazon. they are these kind of inserts. https://www.amazon.com/Kadrick-Threaded-Assortment-Printing-Components/dp/B0CPVCTXJ7/ref=sr_1_7?crid=1DS0TKAV0Y88S&dib=eyJ2IjoiMSJ9.e4BhfopICwDEkURYTqCy3EXTeP0KvjC91w4M6ACDhO8d7aYtxl4VFajV2GwXNcm7w1gX7uBpKIBxXXiq-CEfbcbOAzklWgtghGvM2zE-B6lsUH1gYRs2zEExySfLHsr7TsCxABmrPYm_Xw9yC-Ce7Mkj0VEYY54mFerKZuPuheUXtaZaUzE410cUUSSg4Q5ZhAoKzwv1Q3aBq2hEXHNzyr1PDPztwjevRvu9zuFQYaNf-NPISt7E4922k0aFoHTHhtk7rEc-BWEntOoc49IvtU9ML4BuUNpoRrdu-i8WdUBauGum7TEF8Vx-B7w21M6Ab1V7MCI13J-o8n--fOXTluniH6yVrtxLzR8MgrKHDslukt4fWngLnGf25HwXKJa1NyZxVxQ13Ub0RPrpk5xTpTw3yByDoc6zOBtNvDwCTY1VgpPZKi9kM5vei1HKD05X.zDZSUn8A5gtzHHUzdoTqS0ydzLXEyOLiO994qhVEDWI&dib_tag=se&keywords=threaded%2Binserts%2Bbrass&qid=1734873060&sprefix=threaded%2Binserts%2Bbras%2Caps%2C185&sr=8-7&th=1 and i also used level bubbles and here is a link https://www.amazon.com/Level-Gradienter-Inclinometer-Bubble-Tube-Hanging/dp/B09DYZ2Y9W/ref=sr_1_18?crid=330O3YJAPCE9F&dib=eyJ2IjoiMSJ9.xeUkFby2O_px8bH585_0cjZ1_jv3Ceh5c2zXPDNwcM0elZzUzTuZJz0lUMODL4y0yTxsJQd3UQoL-bYMIWR1u7whVlrv55u75fl6tqYD5vdvzCBli1FwCDS45rWdgZngSUtyCJnjDGjGUOtGPEhnkUqvM5FPLH3DVsU62VRc2cjNMxXH-jZbMJcN3bngdC4icI65B2ricDWC77r_Rwv_rBARJ-EUS1OKbTBaZO5i3IiGNgDezSaz-pco60K445jYMpzlaIs08qPHwkVKmHCFRPt1guF8Yc0Cfv_0_5NuuwtpIYZ0DgsMxfJG3mcjuNrfc-gm0_oU4_K5bg5aO-THNj7_ZbQ31qIFWp_gZw9HkmFhZouK9Kcg2ZQ6EzvCKKsq3FSA_OSeNEFoBHPho_v0W0asbbDruBbk_gn25AeadsXz5mc_Kt6wXepwzBnOsB7b.baWiOYYsNsi4tl87RoDrozkEQZi66eIQVQsns5SZAts&dib_tag=se&keywords=green+level+bubble+35mm&qid=1734873176&sprefix=green+level+bubble+35m%2Caps%2C178&sr=8-18