Special Note - Explanation as to why or why not the 5 wrench set appeared in the 356C tool kit 

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According to the owner's manual, the 356 tool kit only had 4 wrenches. Most enthusiasts believe there is no 13mm ATF nut/bolt in any 356 vehicle, hence, no need for a 13mm wrench. However,  following a collaboration between SAE and DIN officials around 1964, the M8 nut/bolt was resized to 13mm ATF. In the last few months of 356 production ending in July of 1965, the production of the 356C overlapped the production of the 901 (early 911). Those 901/911 cars incorporated the now resized M8 hardware and therefore featured a 5 wrench set. It is a strong possibility that 13mm ATF hardware and 5 wrench sets found their way into the 356C cars/tool kits in these last few months of production.