Tus kheej-tapping 

Lub taub hau countersunk yog suav nrog conical lub taub hau tsim, tus kheej tapping xov, thiab cov khoom hnyav. Tsis zoo li cov ntsia hlau dog dig, nws tsis tas yuav ua ntej tapping ntawm cov xov sab hauv. Hloov chaw, nws ncaj qha rau nws tus kheej hardness rau "txiav" lossis "nyem" cov xov txuas sab hauv ntawm cov khoom sib txuas, yog li ua tiav kev sib txuas sab hauv. Cov yeeb yam no ua rau nws haum rau kev thov cov xwm txheej xws li cov phaj txuas nrog cov phaj nyias nyias thiab rooj sib txoos sai. Cov kev tsim kho dua tshiab uas tau teeb tsa tshuab lub taub hau yog tag nrho submerged nyob rau hauv cov khoom saum npoo yam tsis muaj kev sib cav los ua rau pom kev lossis cuam tshuam. Cov yeeb yam no yog qhov tshwj xeeb tshaj yog nyob rau hauv teb xws li rooj tog tsim thiab cov khoom hluav taws xob ua ke.