Alternatively, you may prefer to glue rare earth magnets into the recess in the hull and to the bottom of the turret. Magnets are a quick and secure way of fixing your turrets to the hulls, but they are a small added expense, which is why the turret peg is provided, leaving the choice up to you.
Rare Earth Magnets (XX105) are available through the online store here... These 1mm x 5mm magnets fit perfectly into the round spaces in the hull and turret.
Above: a finished IS-2 (late 122mm)