Throttle Valve 1.5 small square

Hello,

i have here a z1r carbs to restore but one thottle valve is too damaged on the bottom and need to be replaced.
When i look on the throttle valves i can see a small square on the bottom.
I have other kz1000 carbs and they have not the small square.

I have 2 questions :

1° what is the use of this square ?
2° can i replace this valve by a kz650 1.5 valve that look to have this square to.
3° If i choose to replace the 4 trottle valves by 4 kz10000 ltd valves that have not this square is it a problem ?

On the picture the square is on the top of the valve :

Mikuni use a square as their logo on their jets.
I wouldn't use anything other than genuine parts for such critical components as fuel monitoring. 
Pilot jet size 15 (with a square) is stock for UK 650's. Don't know what is stock for a Z1r so can't say if its a straight swop or not.
The number is the flow rate. Smaller the number lower the flow. 

Mikuni changed the slides a fair bit over the years.  For example, there are various type of 1.5 slides; some are silver anodized, and others are gold, some have a thick bottom and deep pocket for the needle, and others have a more shallow pocked for the needle.  The devil's in the details.  

Yes i know that but because some parts are the same like floats, pins, float bowls ... i try to find a solution without buy this new part that is expensive...

What square?  The notch in the side of the slide?  And if so, what notch?  There are two.

The small top notch on the picture.
Not the logo not the slide