This collection is built on open standards. This page is the key to them: what the nib sizes mean, and which cartridges and refills fit.
Nib sizes
Nib widths run on the standard scale: EF (extra fine), F (fine), M (medium), B (broad). The fountain pens in this collection are fitted with F or M nibs — F for small, precise handwriting and everyday notes; M for a wetter, more expressive line and for signatures. The statement pieces carry 14K gold nibs in F. As a rule of thumb, left-handed writers and writers with small handwriting are usually happiest with F.
Cartridges and converters
Every fountain pen here takes international-standard cartridges (the short/long standard fitting sold everywhere) and is supplied with a converter for bottled ink. No proprietary cartridge is required for any pen in the collection.
Rollerball refills
The rollerballs take the Schmidt Safety Ceramic Roller 5888 F — the standard ceramic rollerball refill — and standard rollerball refills of the same pattern.
Ballpoint refills
The ballpoints take Schmidt P900-pattern refills; several models also accept the G2 format (the standard 'Parker-style' size). Each product page states the refill its pen takes — check there before ordering refills, and note that standards, not brands, are what matter: any refill of the stated pattern fits.
Drawing instruments
The circle tool draws circles from 4.5 to 20.5 cm across, worked with any standard pencil; the ellipse tool draws ellipses and circles the same way. The folding ruler's two 15 cm arms open to 30 cm and set angles from 0 to 270 degrees. The pencil plane shaves a long point onto ordinary wooden pencils — the pencils all of the drawing tools are used with. Full ranges are stated on each product page.
Still unsure what fits what? tinyans@outlook.com — tell us which piece you have and we will name the refill it takes.