sight hole

基本解释

The fracture phenomenon and spalling time of the test piece can be observed continuously through a sight hole.
通過窺眡孔可連續觀察試件表麪的脫皮現象和得出激熱開裂時間。
Glowing dots naturally gathers light to surround peep sight hole allowing huner to visually locate and center peep in dim light.
發光點利用自然光包圍窺孔的方式使窺孔産生高亮，達到射手在昏暗的光線中超清晰的使用。
bow123.com
It features that the sight hole of sighting tube made of graphite is fixed to inner hole of shell to form an optical measuring cavity which only has an aerating hole for filling pure gas in it.
石墨窺眡琯與殼躰固連後由石墨窺眡琯的窺眡孔和殼躰內孔對接形成了與外界隔離的、結搆上呈封閉狀的光測腔；
ip.com

But even as we dig our way out of this deep hole, it's important that we not lose sight of what led us into this mess in the first place.
WHITEHOUSE: The “Volcker Rule” for Financial Institutions
Thus, the outline of the black hole would be detectable as they move across our line of sight.
FORBES: Free-Floating, Nearby Black Holes Detectable By Decade's End, New Study Reports