After the AKM, the Russians switched to the AK-74 and the 5.45x39 round, which as far as receivers were concerned, required very little modification to the Type 4 series. The rest of the gun is a different story however and only 50% of the parts interchange between the AKM and the AK-74 and those are minor parts like pins and springs. The very first AK-74s featured a fixed wooden stock and were simply called the Avtomat Kalashnikova obrazetsa 1974. Note the horizontal groove cut into the buttstock in the picture below. It’s a common myth that the groove was cut into the stock so that soldiers could tell the difference between AKMs and AK-74s in the dark. According to Mikhail himself however, the AK-74 actually turned out to be slightly heavier than the AKM it was replacing, so the groove was cut to bring the weight down.
The first AK-74 rifles were later modified by the addition of plastic furniture. This was done as a result of the lessons learned in Afghanistan, where the harsh environment destroyed the wood used on the original rifles. Here is an AK-74 with the plum, fixed stock. The production run on these was about 3.5 million.
Improving the AK-74 series, the Russkies next added a folding stock to the AK-74 series, and incorporated the improvement to some AKM receivers. This metal, side folding stock turned the AK-74 into the AKS-74 (So skladnym prikladom). This type of stock is known as the Type 2 stock, with the Type 1 being the underfolders.
The last change made was the change from the skeleton stock to a normal looking stock that folded and was made from plastic. This final designation became the AKS-74M or AK-74M (Modernizirovanniy or modernized). This stock is officially known as the Type 3 stock.