From a mixed fleet’s perspective
The filling hatch is the top loading manhole on the crown of the silo — through it PE/PP granulate or other bulk material enters the tank. After filling, the manhole is clamped shut with wing bolts: eyed components the operator turns by hand without a spanner, pressing the cover onto the gasket. It sounds like a detail, but it is precisely these bolts that determine the tightness of the top manhole — and thus the maintenance of working pressure during discharge and the cleanliness of the cargo.
PHS Magnum looks at this hardware from the perspective of an operator handling many brands at once. Most workshops and transport companies do not run a homogeneous fleet — Spitzer, Feldbinder and Kässbohrer trailers stand side by side in one depot, each with its own filling hatches. The good news is that in terms of clamping these brands are similar: they share an M20 thread and an 18 mm eye, and differ chiefly in bolt length. This makes it possible to supply the whole fleet from a single warehouse instead of running separate supply chains for each manufacturer. We run the warehouse in Chorula near Opole exactly with this in mind: complete wing bolt hardware for several brands at once.
Bolt and hardware specification
The range includes three types of components which together form the clamping set for the filling hatch.
| Component | Material | Parameter |
|---|---|---|
| Complete wing bolt | Galvanised steel | 18 mm bolt eye |
| Eye bolt for wing bolt assemblies | Stainless or galvanised steel | All sizes |
| Securing horseshoe | Brass | — |
The range of wing bolt lengths, with brand assignments, is shown in the table below. All items share the M20 thread and the 18 mm eye.
| Size | Brands | Material | Eye |
|---|---|---|---|
| M20x100 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x120 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x130 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x140 | Kässbohrer | Galvanised steel | 18 mm |
Galvanising is the standard finish for a wing bolt — it balances corrosion resistance against the running cost of a component that is replaced relatively often. Where longer corrosion resistance matters (e.g. trailers heavily exposed to road salt), we turn to stainless steel eye bolts. Brass securing horseshoes lock the set in the working position.
Brand compatibility
The wing bolts in our range are assigned to specific brands and their designs — these are not nameless equivalents.
- Spitzer (SF/SK) — the top filling manholes of the SF and SK series are clamped with M20 wing bolts with an 18 mm eye; typical lengths are M20x100 and M20x120.
- Feldbinder (EUT/KIP) — filling hatches appear both on the horizontal, non-tipping EUT and on the tipping KIP silo; sizes M20x100, M20x120 and M20x130 are used.
- Kässbohrer (K.SSK/K.SSL) — for this brand the range includes the longer M20x140 variant.
Since the common denominator is the M20 thread and the 18 mm eye, the difference comes down mainly to shank length. When ordering, it is essential to give the trailer brand and the bolt length — these determine the fit to the clamping stack thickness of the given hatch.
When to replace — signals from operation
Filling hatch wing bolts wear faster than most other hardware, because the operator handles them through every working cycle of the trailer — regardless of brand. In service practice, on Spitzer, Feldbinder and Kässbohrer trailers alike, the same symptoms indicate replacement of the set:
- Corroded or damaged 18 mm eye — makes hand-tightening difficult and risks breaking when clamping the cover.
- Worn M20 thread — the bolt no longer holds the clamping force, so the manhole does not close tightly and loses pressure during discharge.
- Damaged galvanised coating — exposed steel accelerates corrosion and leads to thread seizure, especially under road salt conditions.
- Lost or deformed securing horseshoe — the set loses its lock in the working position.
The remedy is replacement with a complete wing bolt in the correct size, possibly together with a new eye bolt and a brass horseshoe. At every replacement it is worth checking the condition of the filling hatch gasket — the bolt clamps, the gasket seals, so both components work together for manhole tightness and are assessed as a pair.
Chorula warehouse
We keep the full set of wing bolt hardware — M20x100, M20x120, M20x130 bolts (Feldbinder, Spitzer) and M20x140 (Kässbohrer), eye bolts and brass horseshoes — in stock at the warehouse in Chorula near Opole (4 km from the A4 motorway, approx. 180 km from the German border). The location by the motorway and close to the DACH border shortens delivery times both on the domestic market and to customers in Germany, Austria and Switzerland. All warehouse processes are run under an ISO 9001:2015 quality management system.
Matching and order assembly are geared towards mixed fleets: a single shipment can contain bolts for different brands, as well as hatch gaskets and other wear parts. For a set — ask for a quote. Warehouse contact: +48 604 800 869, magazyn@magnumchorula.pl.
What to watch for across brands
The shared M20 thread and 18 mm eye mean that in this category the difference between brands comes down almost entirely to shank length — which follows from the clamping stack thickness of the specific hatch:
- Spitzer SF/SK — the top manholes of the non-tipping and tipping series are typically clamped with an M20x100 or M20x120 bolt.
- Feldbinder EUT/KIP — on the horizontal, non-tipping tank and the tipping silo you will find sizes M20x100, M20x120 and the longer M20x130.
- Kässbohrer K.SSK/K.SSL — for this brand the range includes the longest variant, M20x140.
- Material by exposure — galvanised is the frequently replaced standard, and where the trailer is heavily exposed to road salt, stainless steel eye bolts are chosen regardless of manufacturer.
For a mixed fleet this thread standardisation is a genuine simplification: one fit threshold (M20, 18 mm eye) and a few lengths covering several brands at once. That is why we assemble orders from a single stock, adding bolts for different brands and the hatch gaskets that work with them to one shipment — without splitting the order by manufacturer.
What remains decisive is matching the length to the clamping stack thickness of the specific hatch, not the brand designation alone — which is why when ordering we ask for both the trailer manufacturer and the M20x size. A bolt that is too short will not press the cover onto the gasket, one that is too long will not seat properly; both cases end in a leaking manhole, whether the design is Spitzer, Feldbinder or Kässbohrer.
Specialist portals
A fuller discussion of wing bolts in the context of a specific brand can be found on our dedicated portals: Spitzer and Feldbinder — there we describe the hardware in the context of the SF/SK and EUT/KIP series.
Related categories
- Filling hatch cover gaskets — the sealing element working together with the wing bolts when closing the top manhole.
- Rear hatch bolts — universal rear hatch locking system for the tipping silo.
- Rear hatch gaskets — rear manhole gaskets for silo trailers of various brands.
- Spitzer parts — overview of parts for the SF and SK series.
Author: Aleksy Pasternak — Managing Partner at PHS Magnum, 20 years in the industry, internal auditor ISO 9001:2015 (DEKRA).
