Noun
head space (plural head spaces)
Alternative form of headspace
head-space (plural head-spaces)
Alternative form of headspace
head-space
The solution to this problem, of avoiding overstretching of the brass case, and thereby avoiding the excessive thinning of the wall thickness of the brass case due to case stretching, is to use what is called a "head space gauge". Source: Internet
The tube has to be at least as long as the amount dipping in the mercury + head space + the maximum length of the column. Source: Internet