These FT140-43 ferrite cores marketed by Fair Rite are colour coded using Spectrum Communications unique coding system for ferrite cores being painted half way across the diameter with yellow for type 43, likewise painted blue for type 61.

These toroids are useful as cores for RF chokes or for baluns and wideband transformers where relatively large RF inductance is required but absolute value of inductance is not critical.  The inductance factor is 595uH per 25 turns.

The pack of toroids comes with a two page design sheet for calculating numbers of turns for required inductance using a rating based on 25 turns.  A turn is each time a wire passes through the inside of the core.  On the design sheet is also a table showing how many turns of even gauges of wire from 16 to 34 can fit on two-thirds of the circumference.  The sheet includes two worked examples.

Tracked carriage is quite high.  If you use a computer instead of a mobile phone to order then you can click to buy several items up to a value of 50GBP and ask for an invoice.  I then adjust the postage and return to invoice for acceptance and payment.