Did a bit of a fleet service today. Measured some chains and two of them, both 10sp, need replacement. No problem I have kmc x10, Shimano 10s and sram 10s in the parts bin. Decide to use the Shimano chain for the commuter since it's running Shimano and clever me has noticed that it's a directional chain. Smart boy. Chuck chain on. Logo side out spin it. Works. Genius. Next bike, and I Chuck the kmc on. No problems. So far so good.
Look at previous bike and wonder if directional also means the chain has a 'up' and ''down'. Look at logo and the Shimano is upside down. Wow I'm losing my mind. So shimano chains go have dinner/outer plates and and outside and inside diameter. Take chain off and flip it. What? The writing is still upside down. How the? Take it off and flip it again. Writing is upside down again. Lose my shit. Reach for sram chain. Notice sram chain has logo some facing up, some facing down. Go back to Shimano chain. It too has logos up and down, but seem to be in bunches. Swear.