Spent yesterday afternoon experimenting in my shed. One of the three came undone whilst the other two stayed firm to 4lbs 2ozs before the line broke.The hook was Kamasan B911 to Drennan Specialist 4lb line. Tied with my 1970s Easy-Ti.
Judging from the responses, the chief suspect would appear to be a poor knot ,rather than inappropriate hook/line combination.
I have three of that combination tied up, so will test them to destruction. I hope to establish whether it was a one-off failure or not.
The Drennan 4lb line has a diameter of 0.20, which seems thicker than ideal for a size 12. Clearly was my poor knot tying to blame on those that gave way though.
Playing around with hooks and lines clearly showed the importance of getting the balance between hook/spade size and line diameter.
Interestingly my three old spools of Shakespear Targa (3lb, 2.5lb and 2lb) have the same claimed diameters as the equivalent Reflo Power.
My intention is now to limit spade ends to size 14 and below, with size 12 and larger being eyed.