As a machinist the picture below is one that I have seen thousands of times. This is the inside of a milling machine or machining center. The plate that the die is clamped down to is a tooling plate. These plates can come with equally spaced reamed holes and threaded holes for using with the clamps to clamp die sections down onto. The purpose of the reamed holes is so you can put dowel pins into them and use this as a way to butt up the work piece against so that you will know the work piece is in the machine straight and parallel. For production you can clamp parts against these dowel pins and do a bunch of repetitive work without having to use a dial indicator to indicate every work piece up, increasing productivity.
When I first saw these stones it immediately reminded me of a very early version of a tooling plate that you would find in many modern milling machines. Part of the reason for wanting to go to Puma Punku was to see if any of these holes actually lined up with the patterns on the blocks, at least the ones that looked like they're molded. I was amazed how many did; however there are three blocks with these holes in them and the hole spacings on them are not perfect, some being out by 1/8 of an inch. This would make it hard to correlate the tooling blocks with all of the molded blocks if this is how they were used. Considering what they had to work with they still did a great job. It was still amazing to see how much of the art work or patterns actually lined up exactly with these hole patterns on these "tooling blocks".
In my research before I went to Puma Punku, I found out that there were three of these "out of place" looking blocks that existed with holes somewhat evenly spaced on them. We saw two out of the three blocks, and were sent on a wild goose chase all over 7 different sites at Tiwanaku to find the third stone but never did. Incidentally the two blocks we did find were right on the Puma Punku site, the site that had the most amount of blocks that looked like they were molded. It makes sense to have the tooling blocks where the molds were being made. The picture right below shows the only one of the three blocks I did not find.
This is what I believe is the third tooling bock made.Due to how I think it was used, it could have been refined once they tried a few different shapes and continually refined until they got to this design.
This was the stone I decided to document and test my theory on, due to it having the most amount of patterns. I wanted to see if the tooling block hole spacing measured up the same as the patterns on the block.