The availability of peptide and protein components that fold to defined structures with tailored stabilities would facilitate rational protein engineering and synthetic biology. We have begun to generate a toolkit of such components based on de novo designed coiled-coil peptides that mediate protein-protein interactions. Here, we present a set of coiled-coil heterodimers to add to the toolkit. The lengths of the coiled-coil regions are 21, 24, or 28 residues, which deliver dissociation constants in the micromolar to sub-nanomolar range. In addition, comparison of two related series of peptides highlights the need for including polar residues within the hydrophobic interfaces, both to specify the dimer state over alternatives and to fine-tune the dissociation constants.