section 282 and cap interface 240 by an angle a 1 at an angle a 1 25 degrees the centroid radius r cent2 of the sectional centroid of section 284 is also located between center interface radius r 1 and the smallest outer cap part radius r 3 as shown in fig2 a and 2c in the example of fig2 c the centroid radius r cent2 of the centroid 286 of cross section 284 is shorter than the centroid radius r cent1 of the centroid 283 of cross section 282 at other sections between sections 282 and 284 the centroid is located between center interface radius r 1 and the smallest outer cap part radius r 3 for example a section located at an angle a 1 12 5 degrees and parallel with the cross sections illustrated in fig2 a and 2b i e 282 and 284 returning to fig2 a it should be noted that the side protrusion 280 can assume other geometry and need not extend from the interface 240 parallel to the split line axis 245 for example an edge of the side protrusion 280 can be angled relative the split line axis 245 toward or away from the body part 215 or curved convexly i e toward the body part 215 or concavely i e curving away from the body part 215 the side protrusion 280 can immediately adjoin the outside edge of coupling surface 260 as shown in the example of fig2 a or be positioned elsewhere on the perimeter edge of the cap part 205 spaced apart from the coupling surface 260 fig3 illustrates the connecting rod 200 of fig2 a superimposed on a cross sectional reference diagram of a piston cylinder 305 as shown in reference fig3 the lateral dimensions.