I understand that the Standard Model of QFT treats elementary particles like the electron, quark, photon, muon, etc. as point-like objects. But I've also heard that a "point-like particle" is nothing more than an idealization of a particle. Elementary particles can be treated as point-like objects in experiments because they have no detectable size, but just because we can't detect their size doesn't mean that they have some finite size smaller than what we can detect (I've heard that this scale is about 10-18 meters). Some string theorists have said that elementary particles have a size on the scale of the Planck Length. But "on the scale of" means nothing more than a size that can be expressed in Planck units, as opposed to a specific, well-defined number of Planck units. Are there any theoretical models that predict the sizes of the various elementary particles?