Metric Tap (M5x0.8)

Understanding what the two numbers mean is worth a moment, because it is what stops the wrong tap going into a hole. The M5 is the nominal outside diameter of the thread in millimetres. The 0.8 is the pitch — the distance from one thread crest to the next. Both must match for a fastener to fit. Two threads of the same diameter but different pitch will start, feel as though they are going in, and then bind and destroy the thread within a turn or two. That is why identifying an unknown thread with a pitch gauge before touching it is not fussiness.

M5x0.8 is the standard coarse metric pitch for this diameter, which is what the great majority of M5 fasteners use.

What you actually do with a tap most of the time is repair rather than create. Chasing a thread clears rust, paint, thread-lock or a burr so a screw runs in freely — and a screw forced into a dirty thread is how threads get stripped in the first place. Recutting rescues a thread that has begun to strip. Cutting a new thread in a drilled hole is the less frequent job.

The material is 9CrSi alloy steel, a chromium-silicon tool steel chosen for taps because it takes a high hardness at the cutting edges while retaining the toughness to resist snapping — which on a slender fluted shaft being twisted hard is the failure that matters.

The buyers are engineering and machine shops, vehicle and motorcycle mechanics, appliance and equipment repairers, electrical panel builders, maintenance fitters, and hardware dealers.

Three habits. Use cutting oil generously throughout, since dry cutting tears the thread face and greatly increases the force required. Back off half a turn for every turn forward to break the chip, because a tap jammed on swarf is about to snap. And drill the correct tapping size hole before you start — too small and the tap has too much metal to remove and will break, too large and the thread has no depth and strips immediately. Ask us on WhatsApp for a price, or for a set covering the range.