1973 DT3. I ordered Barnett friction plates and it came with 7 plates, and it says not to use the cushions. I know you don't have to use the cushions (my bike has them), but I have 6 friction plates in my clutch, If you order the stock ones off partizilla, it comes with 7 friction plates eventthough the exploded diagram shows 6 friction plates just like my clutch. What is this extra friction plate for?

Parts diagrams are not assembly diagrams.  Many of the clutch diagrams are flat wrong or misleading...  like on early 125/175 diagrams they often show the stack ending with a friction and they should end with a steel.

In your case, the difference of 6 or 7 frictions is between a 250 (6) and 360 (7).  That's something else that got "lost in translation" when Yamaha went to combined parts lists for similar models on microfiche and from that to the digital parts lists online today.  

If I remember correctly, there is a note in this case at the bottom of the parts diagram that kind of points out only 6 frictions are needed on some models but it's not really clear...  250 had a different "thick steel" than the 360.  

Another trap is the flat thrust bearing comes with a thin washer that is normally not drawn on the parts diagrams. There needs to be washers on both sides of the flat thrust bearing...  often people look at the parts diagram and leave one washer out or put it in the wrong place.    

Thanks!

Here is what Mark is talking about on the thrust bearing ( #17 ) needing a flat washer on each side. It's on the parts diagram but very hard to see. Some are clearer then others. You can enlarge the picture and see it right next to the bearing. (see red arrow). That's because the outer flat washer comes as a set with bearing. see pictures below. 

I purchase clutch plate sets from DG plastic for the DT1 250's and you will get 7 plates as well.  I just throw the extra one in the parts bin and use 6. 









 

I have both washers on there. But now I'm thinking, I replaced every bearing in the cases, had the crank rebuilt, but did not replace that thrust bearing. It felt smooth, but I'm not sure rolling it between your fingers is a good test. Think I will replace it before sewing the clutch side up.

In later years they eliminated that pesky flat bearing. Probably couldn't keep up with supply, as people keep pinching it when it drops down behind the spacer during assembly. Gotta be very careful.