In general, this disclosure relates to a pen housing mechanism, comprising at least one locking collar provided on a pen body configured to receive a pen cap, specifically a pen cap having a plurality of inset “balls” that engage channels within the locking collar. In one form, the “balls” are fit into voids drilled or otherwise provided in a portion of the pen cap and press fit, or otherwise attached, thereto. In one form, a compression spring is provided, which biases the “balls” into a locking portion of the channel.