Hello Everyone,
The rear rim on my 1974 DT250A needs replacement, it is stamped 1.85B x 18  4B 203 . I looked at partzilla and a few other places , unavailable , partzilla  shows the 1973 DT3 shares the same rim , i hunted on ebay and found one,
it is stamped 1.85B x 18 2K 203 , what is the difference in the two rims if one has 4B and one has 2K? because the 73 rim is not samped with a 4B like mine is will it still lace correctly to my 74 hub? I looked up the hubs for both my 74 and the 73 and the first three numbers are different however the rest of the part number does match and with 00-00 meaning no changes? Im still confused trying to understand part numbers any help would be greatly appreciated.
thank You
John

If the rim part number you bought is the rim part number listed for your bike you should be okay.  Rims have date codes and other info stamped in them so not sure if the numbers you're worried about really matter. 

Old paper book says 94418-18051...  but may have been superseded over the years.

Thanks MarkT,
I hope im not irritating  with my rookie questions. i didnt buy the 73 dt3 rim, i just asked the seller what was stamped in it so i could compare it to my 74 dt250 rim because partzilla shows that the 73- dt3 and the 74- dt250 share the same rim. They dont share the same hub according to part numbers.  from what ive read hubs and rims have to mate up , im wondering if they share the same rim but not the hub , how can they interchange ? Or maybe they do ? Since the hub part number for both is the same except the 1st three numbers which i thought indicated the model the part was first used on?  i just want to be sure when i make the purchase the part will fit correctly and since i need to buy spokes too i just wanna be sure. Like you said the two numbers i was concerned about may have a meaning possibly date code? Thanks for the info.
john

Presumably the size of the respective spokes make up the difference between the same rim and different hubs, and vice versa.

Thank you Gr8uncleal ,
So i look up the part numbers for the spokes for the 73 dt3 and my 74 dt250a again part numbers are the same except the 1st three numbers and again 00-00 same parts different number? At any rate, if i try and use a 73 DT3 wheel with a 74 dt250a hub and use 74dt250a spokes it should work ? Im still in limbo

Yamaha lists the part number I listed for your bike.  Don't overthink it.  Lots of parts are interchangeable. 

The spoke angle thing is mostly if you are buying a generic rim that came off of who knows what bike...  which is not what you are doing. 

If the first three characters of the part number are different, then so are the parts (I think that you probably already knew this). The next five characters relate to the type of part, so expect to see the same characters for all spokes. 

If you have the parts that match the numbers for the hub, spokes and rim for the DT250A (regardless of what else they may individually fit) then, to my mind, you have a DT250A wheel.

Edit - Mark posted his response whilst I was typing mine!

thank you both, i get it. found several on ebay that will work.

I’m looking to have a spare set of wheels with road going tyres, does anyone know the interchangeability of wheels/hubs with between models. I have a 1973 RT3 360
Thanks

Front hub for the RT3 is the same as fitted to DT1 E , DT2 , DT3 , and DT 250 A , likewise RT1  . RT2 and DT 360 A .
Only the DT3 , DT 250 A and DT 360 A will have 21" rim as standard fitment .
The rear hub for the RT1 , RT2 is the same as fitted to  the RT3 .