Brigit's crosses and their folklore

Yoda

Many sources say that there is a lot of folklore relating to Brigit's crosses, but few say what the folklore is. It seems clear that the crosses themselves are solar in nature, in keeping with the Fire Goddess' attributes. I'm curious about the folklore, though.

Is there a difference between the three- and four-spoked crosses? Is it held that one must hang them from a loop and ensure that a metal nail doesn't pierce the cross itself? Are there beliefs held about making them or buying them for oneself or for others? Where should one be placed in a house? One or more than one? (Jewish mezuzahs are placed on all of the doorways in a house.) When should they be placed in a house?

Talliesin

I agree that it is a solar emblem, but only because it looks like so many other solar emblems!

I grew up with the four-spoked versions being the only versions I saw (they have obvious additionaly symbolism for Christians who use the same symbol when there are four-spokes). The three spoked version would chime well with Brid as a Goddess with three main areas of responsibility (poetry, healing and smithcraft) and possibly with her being a triple-aspected Goddess, a possibility hinted at by the suggestion that the following chant for curing burns and scalds (occassionaly found used for fevers as well) invokes her:

Three ladies came from the east.
One with fire and two with frost.
Out with fire, in with frost.

I think the above is from the Carmina Gadelica, though I'm not at all sure. It is used both as a Pagan invocation of the Goddess and a Catholic invocation of the saint (sometimes with the addition of "in the name of the Father, the Son and the Holy Ghost").
I never heard of the bit about the nail before. Given that it was hung above the treshold by people who would also fasten horseshoes above the treshold because steel wards the Gentry it seems a bit strange. However in the Christian use of the same symbol one could see how putting a nail into a cross would be seen as a bad thing, so it may come from there. My church-going Catholic mother used to just nail them up though, as did her mother.

We used to make them as gifts for our parents as children, but this was seen as a nice thing to do by our school teachers, and we had no particular desire for them ourselves I don't think they were traditionally gifts, but made within the household in question (see below). Nowadays it's probably more common for them to be gifts.

We would generally place them on a doorway that had people coming through it - people would enter my grandmother's house by the back door, since it was never locked, and that's were there was a Brid's cross, but people entered my mother's house by the front door and that's were she had one. It wasn't seen as wrong to place them elsewhere, particularly in a room that the family would generally gather (living room or kitchen or both depending on your household habits) but a doorway that was much used as the entrance to a house is where you would expect to find one.

Normally the crosses would be given, and hung up, on Imbolc(/Brid's Day/St. Brigit's Day/Lá Fhéile Brid/Candlemas) and ones from the previous year would be burnt. The old tradition was for one person (normally a woman) from the household to gather reeds on the night before and to knock on the door at midnight. The woman of the house would send someone to answer it and then when they entered greet her "Welcome, Brigit". This person would then offer a blessing to all present and crosses would be made. I understand that they would be used in the house they had been made in.