This paper investigates the effect of pointshell shrinking and feature size on manual assembly operations in a virtual environment with haptic force feedback. Specific emphasis is on exploring methods to improve voxel-based modeling to support manual assembly of low clearance parts. CAD parts were created, voxelized and tested for assembly. The results showed that pointshell shrinking allows the engineer to assemble parts with a lower clearance than without pointshell shrinking. Further results showed that assemble-ability is dependent on feature size, particularly part diameter and clearance. In a pin and hole assembly, as the pin diameter increases, for a given percent clearance, assembling low clearance features becomes difficult. An empirical equation is developed to guide the designer in selecting an appropriate voxel size based on feature size. These results advance the effort to improve manual assembly operations via haptic feedback in the virtual environment.