English to Bulgarian Tech/Engineering Electronics / Elect Eng

Spiral Pitch
If the heater is to be spiralled onto the pipe then
follow the circuit route, marking off the required
spiral pitch with a piece of chalk. It may help to
apply string or cord to the specified spiral ratio
and note the resultant spiral pitch before applying
the heaters. If the same pitch is commonly in use
then a stick or rod marked with the spiral pitch
may be a useful gauge.

Спирална стъпка (на резба) или друго?