Many of you already do this, but it might be of use to some who did not grow up in the 60's... :hehe:
For those using monocord or other fairly stout threads (saltwater, salmon / steelhead, etc) a real easy way to thread a bobbin is to but a fresh edge on the thread, start the thread into the bottom of the bobbin cylinder and suck the thread out.
It doesn't work well with multi-filament threads, which I don't like to use anyway because it does not grip feather stems as well (personal preference). My favorite thread is monocord for a variety of reasons when it comes to these big flies and flymaster 6/0 for the small stuff trout eat. It just so happens to thread easily in this manner as well.
But I digress...
If the bobbin becomes clogged, a segment of stout monofilament like 10#, 15# or bigger leader material is very useful in cleaning it out.
Thin mono also makes a good threader in a pinch, push it thru, fold it with the thread in it and start the folded end in the bottom of the bobbin cylinder, then pull on the other end.
Why all this to avoid bobbin threaders? Two reasons:
If you use ruby tipped bobbins for fine threads the "woodstock" method is the easiest and most effective. Metal bobbin threaders do not fit in ruby bobbins and I have no clue where the factory threaders are.
Also, it's much faster to cut a clean edge and suck up the thread than fiddle around looking for a threader with standard bobbins too.
Your results may vary,