|Old Large Cores|
|New Small Cores as Original Planned|
One neat trick that I learned (in the distant past); before winding a DIY bifilar or trifilar wire together, stain one (or more) full length wires with colored Marks-a-Lot pen(s). The enameled magnetic wire takes stain reasonable well. A large felt tip pen and a slightly stretched (taught) wire makes the task easy. After twisting the wires and winding the cores, the stain will help make end identification much easier.
If I remember correctly, pre-stained filer wire is available for purchase, but I like DIY colored stained trifilar wire, because I can use any gauge of wire that I have available.