Drawing cwj mem, raws li cov cuab yeej kos duab, muaj cov yam ntxwv tseem ceeb hauv qab no:
1. Cov yam ntxwv ua haujlwm
Khoom siv: Feem ntau yog ua los ntawm graphite (cov xaum dub) lossis cov xim thiab cov hlua khi (cov xaum xim).
Qib Hardness: Cov cwj mem dub tau muab faib ua ntau qib hardness raws li qhov piv ntawm graphite rau av nplaum, xws li:
H series (Hard): Xws li 2H, 4H, cov hlau lead yog nyuaj, xim yog sib dua, haum rau cov kab zoo.
B series (Dub): Xws li 2B, 4B, 6B, cov hlau lead yog softer, xim yog tsaus, haum rau shading thiab tuab kab.
HB: nruab nrab ntawm H thiab B, dav dav - hom hom phiaj.
Xim xaum xim: nplua nuj xim, nrog softer leads, haum rau txheej thiab sib tov.
2. Cov khoom siv casing
Ntoo casing: Feem ntau hauv cov cwj mem, feem ntau yog ua los ntawm cov ntoo cedar lossis ib puag ncig tus phooj ywg ntoo, yooj yim kom ntse thiab tsis yooj yim rau tawg.
Woodless tsim: Qee cov xaum siv tag nrho cov graphite lossis hloov tau cov hlau lead tsim, uas yog ib puag ncig zoo.
3. Cov qauv tsim
Hexagonal prism duab: Tiv thaiv dov, muab kev tuav ruaj khov, haum rau lub sijhawm ntev ntawm kev kos duab.
Cylindrical puab: Yooj yim los tuav, tab sis nquag dov.
Daim duab peb sab prism zoo: Haum rau cov pib tshiab, pab txhim kho tus cwj mem kom raug - tuav lub cev.