Below is a photo of the two different impulse couplers used on John Deere Magnetos. John Deere changed from long to short lug couplers sometime around 1939.
We've been seeing a lot of JD mags coming in here with the wrong couplers on them. Here's a special note about these couplers; Be sure that your short lug coupler is stamped with "25*" and "6274". If not it's a Wico coupler used on a different type Wico Mag. Take note that there is about a 5 degree difference between these couplers and your Dear Ole Deere will not run right. 5* doesn't sound like much but thats about 10* at the crank shaft! Get it now?