Why nails back out
A spike is a long nail driven through the front of the gutter, through a ferrule (a spacer tube), and into the fascia board. It holds by friction alone. Every summer the fascia swells with humidity and every winter it shrinks; each cycle enlarges the hole slightly and walks the spike outward a fraction. Over a decade of Kansas City humidity swings, that becomes a spike standing half an inch out and a gutter drooping between supports.
Once one lets go the load shifts to its neighbours and the failure accelerates — which is why sagging usually shows up suddenly after years of looking fine.
What we use instead
Hidden hangers with a structural screw. The hanger clips inside the trough and grips the front bead, then a screw drives through the back of the gutter into the fascia. Three advantages: nothing is visible from the ground, the screw holds by thread rather than friction, and the load is carried by the hanger body rather than by a single point on the gutter face.
Spacing matters as much as fastener
A screw every four feet is not a fix if the run needs one every two. We tighten hanger spacing on long runs, on north-facing elevations where ice sits longest, and anywhere a valley concentrates flow into one section. Correct fastener at the wrong spacing still sags.
Can you convert without replacing?
Usually yes. If the gutter itself is sound and the fascia behind it is solid, converting from spikes to hidden hangers is a repair, not a replacement — we pull the spikes, install hangers, and re-pitch the run. If the fascia has gone soft where the spikes have been working, that wood needs addressing first; screwing into rotten fascia just fails again more quietly.