Are you wondering where the odd name for this website originated?
 
Well, PK is very old railway slang standing for Pins and Knuckles.
 
At one time, probably starting sometime during the 1800's, railway cars were connected with link and pin couplers.
 
(There's some heritage equipment still using them.)
 

Basically, the coupler consists of a heavy metal casting attached to the end of each car with a slot where a heavy chain type link is inserted.
 
A pin is dropped through the casting and link on each car so they are connected.
 
A railroad worker had to manually insert the link and pin to couple the cars as they were pushed together.
 

An extremely dangerous position to occupy during a coupling !
 
Most of the old-timers who survived had a missing finger or two.
 
So...  that's where the letter P for pin comes from in OKthePK.
 
As time went by someone invented the so-called North American automatic coupler.
 

While not truly automatic it still requires a person to ensure each knuckle is open before two cars are pushed together, but at least workers don't have to go between cars during coupling.
 
The air brake hoses still have to be connected manually after the cars are coupled.
 
(On modern, truly automatic couplers, the air hoses connect together without human intervention when two cars are coupled.)
 
As two cars are pushed together the knuckles are forced closed by impact and a locking pin drops to lock the knuckles in the closed position.
 
To un-couple a worker does not have to go between the cars, he/she simply lifts a lever on the side of the car releasing the pin and knuckle so the cars can separate.
 
So...  that's where the letter K for knuckle comes from in OKthePK, Pins and Knuckles.
 
One job carried out by today's railway carman, or Car Inspector, is to stand beside the track and perform a visual inspection of a train as it rolls by.
 
If everything is satisfactory he/she will then radio the locomotive engineer/driver saying, OK the PK, or OK the Pins and Knuckles, today's railway slang meaning your visual inspection was good, carry on.
 
Now you know where the name for this railway oriented website originated.
 
Learn more about Car Inspectors, also known as Carknockers, in this article.