SNI or SD — which split housing to choose
Both are split, both take a spherical roller bearing on an adapter sleeve. They differ in the standard they follow, the seat tolerance, the seal supplied as standard and how much they carry. Here are the differences that actually decide.
The short answer
Take SNI when you are replacing an existing split housing or designing to the standard — its dimensions follow DIN 736 and 737, so it fits the seat where an SNL or SN sits today.
Take SD for heavy loads and dirty environments. It comes with a labyrinth seal as standard and a stronger GG 25 housing instead of GG 20.
SNI is about replacement and standard compliance. SD is about load and conditions.
How they differ
Four things really separate them: the dimensional standard, the bearing seat tolerance, the seal supplied as standard and the housing material.
| SNI | SD | |
|---|---|---|
| Dimensional standard | DIN 736 and 737 | manufacturer's own design |
| Seat tolerance | H8 | per series catalogue |
| Standard seal | felt | labyrinth (series 30.. and 31..) |
| Standard material | grey cast iron GG 20 | grey cast iron GG 25 |
| Lubrication | grease only | grease, lubrication holes as standard |
| Stronger variants | GGG 40, GS 45 | GGG 40, GS 45 |
When SN instead of SNI
SN is the same family but to DIN 736 through 739, with an H7 seat instead of H8. A tighter seat means a more precise fit of the bearing outer ring — it matters where guidance counts, not just support.
In practice SNI is enough for most conveyor and fan applications. SN is a deliberate choice.
How much they carry
The catalogue gives the housing breaking load in kilonewtons, separately for five load angles from 55° to 180°. This is not the bearing's load rating: it is the point at which the housing itself fails.
Both series are rated for loads applied perpendicular to the split plane. If the force acts at another angle, the catalogue requires checking not only the housing but also the bolts joining the two halves and the bolts holding it to the foundation.
A GGG 40 spheroidal iron or GS 45 cast steel version raises the breaking load by roughly a factor of 1.8 over grey iron. It is the cheapest way to buy strength reserve without changing size.
Breaking loads in kN are on every housing's product page — at five angles.
What gets forgotten
The bolts joining the two halves are class 8.8 as standard and have their own permissible loads — with an angled force they, not the iron, are often the limit.
On an SNI, a cover plate replaces the seal on one side if the shaft ends inside the housing. On an SD that cover is grey cast iron.
SSNI is the same housing as SNI but with a reinforced base. Standard delivery has no holes in the base — two or four on request.
Source
HFB catalogue 2011/03, page 6 (SNI, SN) and page 34 (SD).