What the mesh numbers actually mean
A designation like 40/60 means the grit passes a 40 mesh screen and is retained on a 60 mesh screen. It is a band, not a single size, and the narrowness of that band is part of what you are paying for. A narrow, well-screened band gives a predictable density of carbide particles at the wear face, which is what allows a repair shop to quote a service life with any confidence.
Coarser numbers mean larger particles: 30/40 is the coarsest of the standard hard facing cuts, 100/120 the finest. Jayanth Tungsten supplies crushed fused tungsten carbide grit in these four standard bands, at apparent density 5.5–6.0 g/cc and approximately 3000 HV Vickers, with other bands screened to order for larger volumes.
Match grit to the abrasive, not to the deposit
The most reliable selection rule is to look at what is doing the wearing rather than at the part being protected.
Large, blocky, angular abrasives — rock in a mining face, gravel in a chute — wear by gouging. They dig in and tear material out. Resisting gouging needs particles large enough that the abrasive cannot get underneath and lever them out, which points to 30/40 or 40/60.
Fine slurries — sand in water, fine tailings, agricultural soils — wear by a polishing action, removing material in small increments across the whole surface. Here a dense population of smaller particles gives a more uniform wear face with fewer matrix channels between carbides, which points to 60/80 or 100/120.
Choosing by deposit thickness instead is the common error. Thickness constrains the maximum grit you can use, but it does not tell you the optimum.
The welding process matters as much as the mesh
Whatever grit you select, the deposition process determines how much of it survives to do any work. Tungsten carbide dissolves into molten steel, and the hotter and longer the weld pool, the more of each particle is lost.
Oxy-acetylene welding remains preferred for much hard facing repair despite being slow, precisely because its lower heat input leaves more carbide intact. Arc processes are faster and better suited to production volumes but dissolve more carbide, and the dissolved tungsten does not come back — it forms brittle intermetallics in the weld metal rather than staying as hard particles at the surface.
This interacts with grit size directly. A fine grit has more surface area per kilogram, so it dissolves proportionally faster. Running 100/120 grit through a high heat input arc process can consume a surprising fraction of what you paid for. If the process is hot, bias coarser.
Standard bands and where they are used
30/40 mesh: severe gouging abrasion. Mining drill bits, rock-contact tooling, large blocky abrasives. The coarsest standard cut, used where particles must be large enough to resist being levered out.
40/60 mesh: the general workhorse for heavy hard facing. Oil-field stabilisers, cone bits, and most mining overlay work. If a shop is going to stock one band, this is usually it.
60/80 mesh: wear-plate cladding and mixed abrasion service where conditions are not clearly gouging or clearly polishing. Also common on thinner deposits where 40/60 would stand proud.
100/120 mesh: fine slurry erosion and thin overlays needing a smoother wear face. Used where surface finish of the deposit matters, or where the abrasive is genuinely fine.
How overlay wear actually progresses
Understanding the wear sequence explains why the grit-to-matrix relationship matters more than grit size alone.
Initially the deposit presents a mixed surface of matrix and carbide. The matrix, being far softer, erodes back first, leaving carbide particles standing proud. Those exposed particles then take essentially all the abrasion — this is the productive phase of the overlay's life, and it can last a long time.
Eventually the matrix behind a particle erodes far enough that the particle is undercut and shed whole. It is then lost without having worn out. The overlay fails not when the carbide wears away, but when the matrix can no longer hold it.
The practical consequence is that matrix wear rate, grit size and grit loading have to be considered together. A very coarse grit in a soft matrix will shed particles early; a fine grit in a hard matrix may never expose enough carbide to do its job. Neither failure is fixed by buying a different mesh band in isolation.