Thanks and you are correct, those are QC marks. Every piece of equipment gets checked several
times before shipping to the rig as mistakes can get costly quick in the oilfield.
The component pictured is a lower end which is installed on a logging tool (google MWD for more info) and 30’ long when fully assembled. Here are a few completed lower ends.
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It is essentially a simple hydraulic valve that amplifies an encoded telemetry signal from the tool string by diverting fluid, then the pressure differential is used for the signal. The full assembly is essentially a GPS for drilling an oil or gas well.
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Here i am disassembling a pulser transmitter that had some signal issues, along with the Rat 1 today, but regarding the lower end its definitely stout enough to fight off Luke Skywalker's real father

.