On my 850T5 the plastic line od is approx. 8.40mm; the exposed part of the barb seems to be .250" , but I can't remember if I could only find 5/16
Home Depot shows them on the website,
"1/4 in. x 1/4 in. Male to Male Barbed Coupler by Freeman"
(the link was obnoxiously huge)
I got mine at Autozone






