[1990 332]

I thought I was told to get 1/4 inch and 3/8. The nipple that comes off the injector is smaller than the inner hose diameter on the 1/4 inch hose

 

[minisub]

Quite a while ago I replaced the pick-up hose with 1/4 tygon. Last month I replaced the fuel filter to injection pump line with diesel rated 5/16 and it fit perfectly. Not sure what lies between the two.

Edit.
Sorry, now I see you are asking specifically about the injector return lines. Haven't had occasion to mess with those but on my various trucks they are surprisingly small.

 

[tmac58star]

The Deere parts catalog shows it to be 1/4 IIRC.

 

[minisub]

Took a look after my mow today. The tubing between the two injectors is not marked, but there is regular fuel hose on the last and it is stamped 3/16.