We found the 4,000lb limit on all double hitch extenders from Wal*Mart to Harbor Freight, to e-Trailer...like the one we have...
Dual Hitch Extender
Less than half the price of the Wal*Mart one.
No straight answer on why a ClassIII (5,000lb) hitch is de-rated to 4K, except assumption that these are like a lever on the receiver and therefore essentially increase the +/- and torque forces placed on the receiver.
Our toad is 3,500lb, plus 400lb dolly...and it is hanging on a 8" drop hitch to get it as level as viable. Have had no problems.
If your toad is under 4,000lb, it should be no issue. But I am no mechanical engineer.
Kim and Steve, Mustang LCDR (Ret), '07 Damon Outlaw #1193
I have seen gross intolerance shown in support of tolerance, Samuel Coleridge
WE LOVE OUR OUTLAW RV