yī sī bù gǒu
not one thread loose (idiom); strictly according to the rules
meticulous
not one hair out of place
bù gǒu
not lax
not casual
careful
conscientious
yī bǐ bù gǒu
lit. not even one stroke is negligent (idiom)
fig. to write characters (calligraphy) in which every stroke is placed perfectly