I keep looking on which way to mount my missing link on my KMC Z50 chain and I cannot find it ....

To me, it looks like the open end should face towards the back of the bike when looking at the top of the chain from the drive side,am i right ?
Or does the orientation does not matter ?

On my other bike, with a KMC x9.99, the missing link looks like unidirectional, thus i am a bit confused with this one

Well the pictured link is a classic master link, not what most would call a Missing Link. the difference is that a master link is for a non der chain, a 1/8" wide chain/cog. Usually found on single speed or internal geared hubs (as there haven't been 4 speed freewheels for a LONG time). A Missing Link is actually a series of connecting links for der chains, 7.8 -5.9mm widths (IIRC). The Missing Links don't have a circlip that slide onto the pins to hold things together. (The master links are too wide for freewheels and cassettes). Connectors Archive » KMC Chain Here's a link to the KMC website which describes some of these links. Andy.

It doesn't matter at all, but for convenience sake 99 out of 100 mechanics install the removable plate to the outside. The slide latch can slide from either direction since there's no stress on it in use.

Like Andrew pointed out, that's not the type of connecting link you'd normally use on a derailleur-equipped bike. The clip that holds the removable plate on makes this link wider than the rest of the chain and it's likely to rub or bind on cogs and derailleurs. If you were going to use a "missing link" on a Z50, it would be like this one. Otherwise, use a chain tool to push out a pin and reinsert it to connect the chain. That's actually the expectation with the Z50 since it doesn't come with a connecting link.

Thanks for all your help guys.
Actually, it's the bike shop that sold me this link since I told them I had a Z50. I guess, I trusted them since bike shops know better than me.

I will try to get the pin out and reinsert it. Not sure what i'm gonna do with the link now...

KMC lists the MissingLink II as being compatible with the Z51 but doesn't mention the Z50.

6, 7, & 8 Speed Connector Archives » KMC Chain

...they make two different pin lengths for 7 and below. I'm not certain which is more appropriate for the Z50.

That's what I did and it went great !

I guess I am confused. I loked at my receipt and it says "3/32 KMC Master Link". So it means I can use it on my Z50 technically since its 3/32 right ?

Yes, and No.

The link might fit your chain, which would be easy enough to check. But odds are very high that it'll be too wide, and rub on adjacent sprockets.

OTOH if you were using this chain on a single or IGH bike, then the link would work fine.

There's 3/32" between your chain's inner plates, and the link may well match that. Your chain's total outside thickness is 7.3 mm and the master link is almost certainly wider than that. Its extra width may not play well in the narrow space between your cogs, or with your derailleurs.

Maybe and no. You might be able to use it on the chain but not in a derailleur system.

They sold you the wrong link... that is for a 1/8 chain.