Chevrolet released the 1/4" deep SS center cap,(where the embossed SS circle decal sits) first,for 1969 production.
These caps needed a rear bolt on retainer to hold them to the center of the rim.The cap part # 3956770,was cast into the back of the center cap.They were used on 1969 AND early 1970 models with SS 14" wheels..My October 1969 built 70 Chevelle came with them.
Sometime around Feb./March 1970,they released a new cap design,part # 3983323..also 1/4" deep,but now with a built in "spring clip" retainer rivited to the backside of the cap itself.It's believed that this new one piece design was cheaper to manufacturer.Unfortunately they would fall off if you went over a speed bump hard enough,and could be stolen easier too with a lil force.
During the mid to late 1970's,Chevrolet released this exact same later "spring clip" retainer cap,but now in a new shallower 1/8" design as service replacements.As the muscle car parts market became more popular,Chevrolet also re-released the 1st design "bolt on" cap again,but this time in the shallower 1/8" deep cap as well,as was it's recent predecessor.That looks like that's what those are in that eBay auction link you posted.
Vehicles built on the assembly line used 1/4" deep caps for both 1969 & 70,in both bolt on & clip on.
Later on GM service replacements were released in both bolt on & clip on design,but both being only 1/8" deep.
Ron Norman @ Mchenry classic car parts hired a machinist to reproduce the 1/4" bolt on caps sometine around 1998.They were really nice,and he later told me he wishes he doubled the order cause they went like hotcakes..He sold them in a plain white 4 compartment box for a reasonable price.No part numbers were ever cast into his,and you can determine his by the striations in the center cap well & edge ridge,from were the lathe cut the centers down to the proper 1/4".
