Outer membrane β-barrel proteins (OMPs) form cylindrical structures that function as pores, substrate specific transporters, and membrane plugs. The structural stability of a β-barrel protein is largely dependent on the interactions between neighbouring antiparallel β-strands. Previously, we characterised one such interaction, the mortise-tenon joint. Formed from the interaction between a luminal aromatic residue on one β-strand and a glycine on the adjacent β-strand, mortise-tenon joints were shown to contribute to the folding and stability of the Pet autotransporter β-barrel. Here we survey the prevalence of these mortise-tenon joints in all OMP structures. The unique 60,90 chiral 1 and 2 angles, which are a definitive feature of the tenon side chains, were used to screen the Protein Data Bank for tryptophan, tyrosine and phenylalanine tenon joints. Mortise-tenon joints were then confirmed using structural analyses. The frequency of mortise-tenon joints was correlated with the biological function, size, and number of β-strands of each structure. Our results indicate that mortise-tenon joints are highly conserved within OMP families and that the number of mortise-tenon joints vary between different OMP families. In addition, we found that β-barrels involved in the transportation of proteinaceous substrates have a high frequency of mortise-tenon joints. In contrast, we observed that mortise-tenon joints are under-represented in small β-barrels, which form plug structures, and in β-barrels that employ other mechanisms of stabilisation, such as oligomerisation. Our results are discussed in relation to the structural requirements of OMPs and the possible role of mortise-tenon joints in β-barrel stability. Understanding of inter β-sheet interactions and their role in β-barrel stability is also important to the rational design of synthetic β-barrels.