My d4 has serial # -2T466WSP- does anybody know what the WSP means? Thanks jim

Wide Track. Special Parts. WSP The special parts are internal items relating to gearing usually and not bolt on items like PTO etc.

On D4 Specail parts can mean lots of diff external parts (wide topseat,sideseat,tailseat,side exaust,OD green paint,long trackframes,type of fenders,grill gaurd,type of seat, hood air intake, type of track pads, ECT) many things. In that era of D4 had ony one trans group. The bill of sale for my 2T5916 says Specail Parts installed were US War Dept. paint group(ODgreen green paint&seats) & tailseat group(All parts for tailseat arrangment)

Always has been some confusion about the "SP" designation.
Apparently the D4 started out with almost anything added as Special Parts then later changed to transmission and final drive gears only.

Thanks Guys for all your help-- I just love these old Tractors I dont know all there is to know about these old tractors but it sure is nice to know people that do-- this is my first old cat to own and as soon as my wife gets over the "Shock" [ she thinks ive gone nuts] i,m gonna find me a 3t 7. then she will go nuts Thanks Jim