These have made the Christmas present slot for this year amongst my kids and their cousins (10 units). All in different mixed woods from wood and veneer I had around, and with varying designs such as deliberate slanting. All of these have 7mm brass tube (Turners Retreat 10") cores with ends with 12mm turned extensions glued into the barrel tubes, with a 4mm hole in the writing end to accommodate the Bic 'refill'. It is surprisingly easy to cut (with a sharp parting tool) the cylinder extension on the pen end even though the resulting walls are only 1mm thick (that is 6mm dia 12mm long extension with a 4mm hole drilled before turning).
Boxes are low-cost (£18 for 24) pen boxes from Amazon ('Emartbuy Set of 24 Brown Cardboard Jewellery Pendant Boxes, Pen Boxes').