Correct

内壁

/ nèi bì / 
Strokes

Example

As a Noun

inside/inner wall; inwall

1
Qìgāng
汽缸
nèibì
内壁

the inside of a cylinder

2
Bōli
玻璃
guǎn
管
nèibì
内壁

the inside wall of a glass tube

As a Noun

intine (of a spore); endospore