Oil

Four lines, fully recovered: gear and engine oil in two entries, and silicone and hydraulic oil in two entries, with grease carried alongside them under Others. A four-line lubricant range is a deliberate position — it covers the fluids a maintenance store must have on the shelf, and leaves the specialised grades to be ordered against a specification.

Gear oil

Gear oil exists as a separate product from engine oil because the load case is different. Gear teeth meet in a rolling and sliding contact under extremely high local pressure, and the oil's job is to keep a film between two surfaces that are actively trying to squeeze it out. Gear oils carry extreme-pressure additives that react with the metal surface under load to form a sacrificial layer — protection by controlled chemical reaction rather than by film thickness alone.

This is also why gear oil should not be substituted casually. Some extreme-pressure additive packages attack the yellow metals used in worm gears and bushings, so a gearbox with a bronze wheel needs a formulation compatible with it. The consequence of getting it wrong appears months later as a worn wheel, not immediately.

Engine oil

Engine oil does more jobs than any other fluid on a site: it lubricates, it cools, it seals the piston rings, it neutralises acidic combustion products and it holds soot in suspension so that it reaches the filter rather than settling. Most of an engine oil's specification is about those secondary functions rather than about viscosity.

In an industrial catalogue engine oil is stocked for standby generators, compressors, pumps and site plant rather than for a vehicle fleet, and those applications share a problem: long idle periods punctuated by demanding duty, which is hardest on the oil at start-up.

Hydraulic fluid

Hydraulic oil is a power transmission medium first and a lubricant second. It must be almost incompressible, it must maintain viscosity across the operating temperature range, and above all it must stay clean — the majority of hydraulic system failures are traced to contamination rather than to component wear. A few particles of the right size will erode a servo valve's control edges and gradually change the way a machine behaves before anything fails outright.

Water is the other contaminant that matters, because it destroys the additive package, promotes corrosion in the reservoir and causes cavitation damage at the pump. This is where the aluminium sample bottles elsewhere in the catalogue connect: routine oil sampling and analysis is how contamination is found while it is still cheap.

Silicone fluid

Silicone fluid is not a general lubricant and is not a substitute for one. It is used where an ordinary mineral oil would fail: very wide temperature ranges, chemical exposure, electrical duty where dielectric properties matter, and as a release or damping fluid. It is chemically inert, thermally stable and — a practical warning worth recording — extremely difficult to remove from a surface. Silicone contamination on anything that will later be painted, bonded or coated causes adhesion failure, which is why workshops that do finishing work keep it strictly away from those areas.

Handling and storage

Three practical points cover most lubricant problems in a store. Drums stored outdoors on their ends collect water in the top rim, which is then drawn past the bung seal as the drum breathes with temperature change. Decanting equipment used for more than one product cross-contaminates them, and a dedicated pump or jug per product is cheaper than one wrong fill. And oil has a shelf life — additive packages settle and separate — so stock should rotate rather than accumulate.

Classification and test methods for lubricants and hydraulic fluids are published by ASTM International, and viscosity grade systems are maintained internationally by the International Organization for Standardization.

Related: Others for grease, bushes and couplings, and Pipes & Pipes Fitting for the hoses, flare fittings and hydraulic connections these fluids run through.