I got an explanation from the DRGW list as to why the idler flats didn’t have stake pockets.
Hi Doug
The idler flats were only used between pipe gondolas when handling long
pipes. They were not intended to carry any loads at all. The idler flats
were converted from other type of cars not needed anymore. To put on stake
pockets would have increased the costs without much benefit. Rio Grande had
a surplus of cars for other loads at this time.
Roland Levin
Stockholm, Sweden