What is a ring spanner?
A ring spanner is a simple, double-headed, single-piece spanner with a profile set in a looped head.
How does a ring spanner work?
The loop is placed over the head of the fastener and the spanner profile pushes against the flat sides of the fastener head to turn it.
Ring spanners are less likely to slip off the fastener than open-ended spanners because they make contact with the fastener on all sides. This means they can be turned in wider arcs more easily, making the task quicker.
What are the different types of ring spanner?
The most common ring spanner profile is the 12-point (or ‘bi-hex’) profile, so-called because it has 12 points and troughs.
12-point profiles allow spanners to lock onto fasteners in a smaller space than a 6-point (hexagonal) profile does, allowing the fastener to be turned further before the spanner needs to be readjusted.
6-point profiles can only be used on hexagonal fasteners while 12-point profiles can be used on hexagonal or square fasteners. Other profile shapes are available but they tend to be specialised for one job, such as an immersion heater spanner.
The shape of the profile varies slightly between manufacturers and some have designs that are less likely to damage the fastener because they make better contact with the fastener sides. Designs you may come across can be referred to as ‘OGV’ or ‘AS’ (anti-slip).
The heads of most ring spanners are at a 15 degree angle to the shaft. This gives better access into some recesses, as well as making it easier to hold the spanner without the user’s fingers getting in the way when turning a fastener on a flat surface.
Some ring spanners are also ‘cranked’ which means the head is offset from the shaft. This also helps with access into recesses and makes it easier to turn the spanner without damaging the user’s fingers!
How else are ring spanners measured?
Ring spanner sizes are given as the size of head of a hexagonal fastener the spanner can be used on. Ring spanner profile sizes are available to fit hexagonal fastener head sizes ranging from 4mm to 50mm or 5/32″ to 2″. The spanner length increases with the size of the spanner head, from about 100mm (4″) to 500mm (19½”).
To choose a size of ring spanner for square fastener heads, increase the fastener head size by 25% to find the approximate size of a suitable 12-point ring spanner. For example, a square fastener that has a 12mm head requires a 12-point ring spanner with a given size of (12×1.25=) 15mm.