Distributore BUMAX ITALIA
Viti Bulloni Alta Resistenza Meccanica


MarkingThe stock range of hexagon head bolts and screws socket head cap screws, Hexagon nuts and Bumax lock nuts are normally marked in accordance with the figure below.Example:

Dimensions < M5 do not contain some of the marking due to space restriction.
Sub-contracted products may have different marking.
The steel grade is normally marked.
Manufacturers mark (BUMAX®), steel grade (e.g. A4 -316L), and property class (e.g. 80).
Property classes and marking in accordance with ISO 3506. Note the difference in property class designation between Stainless steel and carbon steel fasteners.
Imperial threaded fasteners are not covered by ISO 3506 but we follow the ISO standard as well were it is possible.

Our products are supplied bright or passivated, which gives the best corrosion resistance. The Bumax 88 programme of nuts and washers and the full range of Bumax 109 are supplied treated with lubricant in order to avoid thread galling.
Bumax Hard is supplied coated, M8 lubricated in addition.
All lock nuts, both Nylon insert and Bumax Lock are supplied lubricated.

Choice of material:
Stainless steel A2 can be used in combination with most Stainless steel grades with similar or lower corrosion resistance.
A2 is suitable for outdoor applications but not in coastal areas and only to a limited extent in oxidising acids.
A4 is suitable for outdoor applications also in coastal areas and for normal corrosion expose. Bumax A4 – SS14.2343 / 316L HiMo can also be used to a limited extent seawater containing chlorides and in non-oxidising acids.
For harsh corrosive conditions, we recommend that material is selected in consultation with our engineers or those at the steelworks.
Examples of commonly occurring Stainless steels are:

Ferrit-autenitic steel:
EN 1.4462 = Sandvik SAF 2205 = UNS S31803 (Duplex).
EN 1.4410 = Sandvik SAF 2507 = UNS S32750 (Super Duplex).

Austenitic steel:
Avesta 254 SMO = UNS 5 3124, EN1.4547.
Sandvik SANICRO 28 = UNS N 08028 = EN 1.4563.

Autenitiska stål for use at elevated temperatures:
SS 14 2570 = AISI 660.
EN 1.4835 Avesta 253 MA = UNS S30815.
Sandvik SANICRO 30 = UNS NO 08800.
Sandvik SANICRO 31 H = UNS NO 08810.
EN 1.4845 SS 14 2361 = AISI 310.

EEN 1.4462, 4410 and to some extend SS1.2324 are suitable for machining of fasteners and components were high strength and low elongation co-efficient is required and were this cannot be achieved with Austenitic Stainless steel.
SS 14 2570 is an Austenitic Stainless steel for use at elevated temperatures with excellent mechanical properties.
SS 14 2361 (SÅ3) is a heat resistant Stainless steel.
SS 14 2302, 2303 (Cl) and SS 2321 (C3) have limited corrosion resistance but can achieve good mechanical properties through hardening.

Self-tapping screws (sheet metal screws)
We stock self-tapping screws in steel A2, A4 and A4 ss14.2343 / 316L HiMo.
The steels have good corrosion resistance and are designed for normal corrosive conditions. The screws can easily be fitted to all plastics and light metals. When used in low and high alloy steel plate the threads can be deformed due to deformation hardening from the punching or the drilling operation.
When the material thickness is > 0,5 x the thread pitch material hardness may not exceed 115 HV.

In 1983 ISO issued a revised thread standard for self-tapping screws, ST-threads, “ISO 1478-1983 Tapping screw thread”.
The change in dimensions is marginal and concerns a reduction in the lower limit for the outside diameter.
One important change is however, that the thread must be specified by the thread diameter. A specific screw may therefore be designated ST 3,5 x 19 were ST stands for self-tapping, 3,5 for the outside diameter of the thread and 19 for the screw length.


Conversion between the two system is as follows:

5T2,2 5T2,9 5T3,5 5T4,2 5T4,8 5T5,5 5T6,3
B2 B4 B6 B8 B10 B12 B14

ISO Type C = cone end. ISO type F = flat end.

When material hardness HV > 115 we recommend Bumax Hard or if the corrosion exposure permits, screws made from C1 steel which are manufactured as special to order.
For more information about Bumax Hard ST screws, please look at “Bumax Hard Taptite and ST”.
The friction problems with Austenitic Stainless ST screws can be considerably reduced by surface treatment or by lubricant.

When assembling Stainless steel joints, a very low revolution screw-driving machine is required or preferably the screws should be tightened by hand. Punching machines should not be used.
In very unfavourable assembling conditions, MoS2 or suchlike lubricant is recommended.
If considerable galling problems occur when assembly, please contact our technical customer service.

BUMAX Lock is a special all metal lock nuts: The special feature is the designed thread profile making the nut free spinning and locks when tightened.
Note that a higher tightening torque than for standard nuts is required.

Taptite and Plastite:
Taptite is a thread forming screw for use in soft material such as light metal and plastic.
Bumax Hard Taptite is developed for use in steel and Stainless Steel.
Plastite is a thread forming screw for use in plastic. Both Taptite and Plastite have a trilobular cross-section and excellent function.