For some reason, I find this an attractive example, even though I don't think they provide instances of EC.
For the advocate of EC, however, the situation is more interesting. There seems to be an issue of whether or not these could count as tools wherein cognition might extend. As I've mentioned before, I think it is Clark's view that tools suitable for EC must be information resources or information processors. I get this as implicit in Clark's conditions on "trust and glue". Here is one version of them:
1. The resource must be reliably available and typically invoked.The information requirement is implicit in conditions 2. and 3. So, are the handaxes tools like a recipe or like an oven used in baking a cake? For me, the answer is no, but for the advocate of EC it seems to be up for grabs.
2. Any information retrieved from the resource must be more-or-less automatically endorsed. It should not usually be subject to critical scrutiny (unlike the opinions of other people, for example).
3. Information provided by the resource should be easily accessible as and when required.
Malafouris, L. (2010). "Knapping intentions and the marks of the mental" In. Malafouris, L., & Renfrew, C. (Eds.). (2010). The cognitive life of things: Recasting the boundaries of the mind. Cambridge: McDonald Institute Monographs.