Tapered leaves gradually narrow towards the tip. They tend to be shorter than straight leaves. The leaves have smooth rounded edges for comfort and safety when handling.
Tapered leaves allow measurements to be taken in tight awkward spaces because of the slip taper design. For this reason they are often preferred by mechanics and servicemen.
A tapered feeler gauge has a small tip radius. Here the gauge fits into the wear gap and does not bridge across it. This allows the correct measurement to be taken between the rocker and the valve stem.
The smaller width design means curved surfaces may roll across the tapered edges as the gauge slides into the gap. The two surfaces either side of the gauge’s tapered tip may move so they become closer to the blade edges of the feeler gauge.This would not be reflected by the measurement. Tapered leaves are best suited to measuring small width clearances. (Where parts have to be a set distance apart for only a short distance).