Custom Stool Slot Pencil Holder £20-£30 quid

I have a wooden stool with huge dowels and I want to attach an assembly that can allow a pencil pot to be slotted onto the wooden dowel ( see photos ) the whole point is the pencil pot is able to be detached and removed when needed. There are two parts that need to be designed.
1. The immovable base which will be permanently attached to the stool ( maybe with glue/nail)
2. The pencil pot with a slot ( see photos)

Here is what I already know and need captured in the 3D file:

• Material: plastic only, so please model wall thicknesses and fillets with FDM/FFF printing in mind.
• Form factor: one circular compartment, 12 cm tall, 7 cm internal diameter. No extra dividers.
• Fitment: the outer geometry must seat snugly with the immovable base on the stool; I’ll give you the slot’s exact dimensions and a quick phone-photo sketch once we start.

Deliverables
1. Editable CAD (STEP or Fusion 360)
2. Print-ready STL with units in millimetres
3. A quick shaded render so I can preview the look in situ

Acceptance criteria: the STL opens error-free in PrusaSlicer, dimensions match the spec within ±0.2 mm, and the file passes a standard manifold check.

If anything about the slot geometry affects draft angles or undercuts, flag it early so we can adjust before finalising the model.