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I noticed 7 tooth D bore sprockets for # 25 exist and they are for sale online.  What motor do these mount on?  I am wondering if that motor will fit on the E-100 so I can use it instead of the stock motor with the 9 tooth motor sprocket.

Also, is there any way if the D bore is too small on this 7 tooth sprocket, to make it larger to fit on the stock E-100 motor?  Can I take a dremel type tool and very slowly and carefully nip out a new larger D bore or would I have to take this to a machinist to get it done?  I think 7 and 55 tooth sprockets would be almost ideal for offroading because it would drop the top speed from 10 mph to about 6.6 mph (to about 2/3rds of stock speed).  That is very significant and should help greatly.  Thanks for any helpful info.

The sprocket is 6mm and is advertised on Ebay for electric motors but doesn't specify which.  I would like to know what motor has a shaft compatible with this sprocket.  My E300s currently has 9 and 89 sprockets on it but could use even more reduction for riding on grass so I would like to try this 7 tooth.  I'd be willing to change the entire motor if it is similar in power and input voltage but if not, I am wondering if it is possible to just change the motor shaft to accommodate this sprocket.  It is a shame they don't make more sizes of front sprockets compatible with the E-300s and other similar electric scooters.  9 front is not small enough for me and I am already close to the max size that will fit on the rear (89 teeth).

That is not what I asked.  I am asking what electric motor has the shaft I need to fit the 7 tooth sprocket because it may be easier to just change motors on the E300s to get the reduction I desire.

Unfortunately, just replacing the motor to this one and using a 7 tooth sprocket instead of a 9 tooth wont help the Razor E100 scooter much or at all because of the higher RPMs of this motor.  I wonder if the shaft could be replaced such that this shaft pictured could be put on a slower spinning motor such as the stock E100 motor which I assume spins at around 2500 RPMs.  The idea is to lower the load, the top speed, and the "pushoff" speed of the scooter without having to spend a lot of money on it.  It is a shame that the E-100 doesn't come stock with the smaller shaft that accepts this 7 tooth sprocket.  That would be nice since the stock 47 tooth rear sprocket is already large compared to the size of the tiny rear wheel.  Again, this is for small kids that are just learning to balance a bike so there may be training wheels on the scooter.  The lower speed would be very beneficial to them while learning.

  The only other idea I can think of is to use an 8 tooth sprocket (which I already have) with the same bore as the E-100 motor shaft, and somehow use 1 or 2 set screws to prevent the sprocket from slipping on the motor shaft.

I just checked my 8 tooth sprocket and it appears it has about 1/4 inch (6.35mm) bore so I am wondering if it could be widened to the size of the E100 shaft and held in place with 1 or 2 set screws on the flat part of the motor shaft.  It is only a 100 watt motor so there is not much torque.  Dropping 1 tooth on the front sprocket is equivalent to adding 6 or 7 to the rear, but with better turning clearance. 8-55 sprockets on the E-100 would drop the top speed from 10 MPH (9-47 stock sprockets), to about 7.5 MPH.  It would also likely feel "snappier" and work better on packed dirt.  This is worth trying in my opinion.  I will have to get another E100 and make this work.  Anyone have advice for me?  Pitfalls to watch out for?  Should I use 1 or 2 set screws?  Will it hold?  Since there is only one flat spot on the motor shaft, can I put 2 set screws there side by side on the sprocket?  Notice from the attached pic that the sprocket is not just "flat".  There is plenty of depth to it to allow room for set screw(s).  That entire depth though would have to be bored to the right diameter to allow it to slide onto the E-100 motor shaft.

  Also, to make the D bore, could the sprocket be bored to a round hole and then material added back in to make the D shape bore such as welding a straight chord (geometric definition) across a portion of the round bore?

Okay thanks for the reply.  It sounds like this is worth the effort to try to get working, provided the cost of boring the sprocket to the proper hole diameter and getting the set screw to work is not too expensive.  

Also, a good side effect of lowering the top speed of a scooter is it extends the runtime between charges and increases the mileage between charges too.