A dense, high-speed interconnection may be formed with a mating header and receptacle connector. The header connector may have groups of mating contact portions extending from the connector housing. Structural projections may extend from the housing adjacent some or all of the groups of mating contact portions. The groups of mating contact portions may be signal and ground mating contact portions associated with a signal pair. The groups may be arranged in an array and the structural projections may be arranged in an array intercalated with the array of the groups of mating contact portions. A receptacle connector may include an array of apertures configured to receive the structural projections. The structural projections may be shaped and positioned to reduce damage to the mating contact portions of the header connector, enable reliable manufacture, and to provide a high-density mating interface.