The AK-47 configuration features a plastic AKM/74M handguard and a plastic stock. The AK-74 configuration features a wooden handguard and stock, while the AKS-74U configuration features a wooden handguard and a metal wire stock. The AKS-74U's barrel is only 8.3". In comparison, the AK-47 and the AK-74 both have much longer barrels, both at 16.3".
The AK-47, AK-74 and AKS-74U all use very similar components, the main differences being the handguards, stock and barrels. However, the AK-47 and the AK-74 also use different magazines. The AK-47 uses curved metal 30-round magazines by default, while the AK-74 uses a slightly less curved plastic 30-round magazine by default. The AKS-74U uses the same magazines as the AK-74.