hydra427 wrote:Idris, obviously there are two different types of rivets here, can you give me a little insight as to the difference and what made you ask the question in the first place?
The suspicion is that the first baseplate casting was not strong enough to take the pressure of the riveting machine, resulting in too many rejects (i.e. damaged models). Lesney therefore went over to punching the rivets until the casting could be modified.
Having said that, I have the idea that there are two types of spun rivet on the first-type baseplate: a normal one and a very shallow, almost saucer-like one. If so, I would suggest that the latter represents a low-pressure solution to the riveting problem. However, more research is needed before this can be stated with any certainty. (Comments and photographs are welcome.)
Incidentally, there are only two other models with punched rivets: early M5a Combines (above the rear axle) and early M10a Dumpers (the pivot).