Take a length of strong thread (seine twine, cotton), measure twice the length of the lower shaft bar plus a few inches extra. Thread it through the small hole at one end of the shaft bar (front to back), take it along the length, in back, thread through the small hole at the other end (back to front), and tie the ends together at front center. Make sure the string, both in front and back of the lower shaft bar is OUTSIDE the heddles. This will keep the bottom of the heddles from sliding off. If you place the string inside the heddles, they will slide off. This works for both Texsolv and string heddles.
I usually use this method on my looms. Not long ago I moved heddles on my countermarche, and neglected to put these strings on my CM shafts. Yes, a few heddles went sliding off the lower shaft bar. I was finishing weaving the hem of a towel and didn’t notice right away that the first shaft was hanging up on the right side. After removing the temple, I found a few floats at the right side of the hem which were easily repaired, but could have been avoided. These strings will be back on every shaft on the CM loom before I begin weaving again on Wednesday.
Tuesday? Socks, all day!