Knitting Mechanics
Transfer holes are not a needle fault. They are a loop that was asked for more yarn than its neighbours could lend.
— %
How close the robbed loops run to failure
The required loop length is a geometric minimum: two legs across the span plus the yarn passing round the receiving needle blade. It ignores the transfer point or spring, which on many machines carries the loop part of the way and reduces the demand, so the figure is conservative for those machines. The robbing span is entered rather than derived because it depends on yarn friction, ground structure and fabric tightness in ways no single expression captures - it should be treated as a modelling assumption and, where transfer performance is being diagnosed seriously, established by testing rather than assumed. Strain is distributed evenly across the robbing loops, which real yarn does not do exactly; the loops nearest the transfer carry more, so the peak strain is higher than the figure reported and the margin is smaller than it appears. Breaking extension should be the value at the knitting strain rate, which is higher than a standard tensile test measures.
Rib & Interlock Loop Transfer Strain, Tightness Limit and Speed Cost — free, with the formula and a worked example, at Textile School.