Astanga Hrudaya
मूलाग्रेऽङ्गुष्ठकोलास्थिप्रवेशं धूमनेत्रकम्। तीक्ष्णस्नेहनमध्येषु त्रीणि चत्वाति पञ्च च॥८॥
The length of the tube should be 24 Angula (width of one knuckle) for Mrudu (soft, Sneha) Dhuma 32 Angula for medium Dhuma and 40 Angula for strong Virechana Dhuma Pramanam तीणं - 3 x 8 नेहनं - 4 x 8 मयं - 5 x 8
english translation
mUlAgre'GguSThakolAsthipravezaM dhUmanetrakam। tIkSNasnehanamadhyeSu trINi catvAti paJca ca॥8॥
hk transliteration by Sanscript