L – piston length 

H – distance from piston bottom to the axis if pin holes in bosses

H_p – distance from piston bottom to the zone where skirt diameter must be measured

d_k – diameter of groove in the bottom of pistons of petrol engines or diameter of combustion chamber of pistons of diesel engines

d_r – diameter of combustion chamber mouth of diesel engine pistons

h – depth of groove in the bottom of pistons of petrol engines or depth of combustion chamber of pistons of diesel engines

R – radius of semi-spherical combustion chamber of pistons of diesel engines

S – displacement of axis of piston holes in bosses from the piston axis

d_п – diameter of pin holes in bosses