There are many advantages and benefits to using HAM-LET Let-Lok Double Ferrule fittings as many of our customers are now experiencing. But not everyone knows or understands these benefits so in this article we will highlight some of them, in no particular order;

Stacked Tolerances

All HAM-LET components are machined from high quality traceable bar stock materials to exacting tolerances. This ensures that each fitting will perform its intended function without compromise in the most demanding application areas.


Consistent repeatable gaugeablity in the HAM-LET tube fitting is an important safety feature.  The installer can be assured that the fitting has been correctly pulled up without the need for complicated torque figures and charts. Likewise, the installer does not rely on “feel” which can vary according to tube hardness and wall thickness.  Gageabilty is a simple easy method of ensuring that the fitting will hold pressures high enough to burst the tubing.

Standard Installation Procedure

Removes the need for the installer to remember various complicated assembly procedures, promotes safety together with faster lower cost installations.

No Special Tools Required

No need for torque wrenches, flaring tools or special spanners. Standard open-ended spanners are all that is required to pull-up HAM-LET fitting from 1/16” to 1” OD and the equivalent metric sizes. HAM-LET can be installed in confined areas without the need for costly and cumbersome tooling.

Self Aligning

Unlike other types of fittings, it is not necessary to disassemble HAM-LET fittings to assemble onto the tube. The practice of removing the fitting nut etc and placing them on the tube is time consuming and can result in lost components or damage to the sealing surfaces. Simply inserting the tube through the nut and ferrules of the HAM-LET fitting saves man-hour costs and prevents incorrect assembly.

Low Pull-up Torque

A common problem associated with tube fitting installation is under-tightening. This is especially true when using and hard and heavy wall thickness tubing. HAM-LET’s unique ferrule action eliminates high torque pull-up allowing the installer to safely accomplish the standard installation procedure quickly and without the need for a great deal of physical effort. More fitting pull-up per man hours are achieved thus generating higher productivity.


HAM-LET, tube fittings swages the tube without damaging the sealing surfaces. This means that the fitting can be remade many times while still maintaining high leak tight integrity and without having to replace component parts. Significant cost savings can be realised by reclaiming used fittings for new installations.

Tube Supported ahead of ferrules

Vibration and impulse shock can adversely affect the sealing performance of any fitting that is not correctly supported. The HAM-LET tube fitting is designed to support the tubing ahead of the ferrules. When the fitting is pulled-up the tubing, through the swaging action, expands into the body bore providing an anti-vibration holding mechanism that greatly enhances the sealing integrity in severer system application.

No Torque transmitted to tube

Tubing can be subject to early fatigue failure from the “twisting” action when installing bite or flare type fittings. Fatigue failure is common in these types of fittings and the twisting action can breakaway fittings that have already been installed. The back ferrule in the HAM-LET tube fitting has a number of functions, one of which is to act like a “slip washer or slip ring”. When the HAM-LET fitting is installed all the action in the fitting moves forwards, there is no rotary motion to cause damage or early fatigue failure in the tubing.

Does not Cut or Weaken the Tube

Bite, compression, flare and multi-grip types of fittings are all designed to in such a way that if sufficient torque is exerted to the nut the “olives” or “sleeves” will either bite through the tubing or significantly weaken the tubing.  This is especially true if vibration or impulse is present within the system. HAM-LET, as the name suggests, through the actions of the precision ferrules, actually cold works the tubing to create a flareless mechanical grip. This action ensures that the full wall thickness of the tubing is utilised to contain system pressure and allows for the use of tubing of various wall thicknesses. In addition, the HAM-LET ferrules cannot be forced through the tube wall by over-tightening the fitting. The user can purchase thin wall tube for lower pressure application and consequently save on material costs.

Used on Thick or Thin wall tube

Bite type fittings are generally used on thick wall tubing because of the way in which the olive’s “Bite” into the tube to create the seal. If these types of fittings were installed on thin tubing the chances are that the olives would bite or cut through the tubing or leave it in a weakened and dangerous condition. It is common to find expensive thick wall tubing been used on low-pressure systems solely to accommodate the selection of this type of fitting. Likewise, flare fittings are normally associated with thin wall tubing and low to medium integrity systems. The reason for this is that it very difficult to consistently flare thick wall tube without damaging the seal area. The design function of the HAM-LET ferrules and the inter-action of the ferrules, overcomes the variables of different wall thickness allowing a broad range of tube to be used without modifying or changing the ferrules.

Used on Hard or Soft tube

Depending on the hardness of the tubing to be used, some tube fitting manufactures will offer the user several choices of olives and tube inserts to prevent the tube wall collapsing. Because HAM-LET is designed to “swage” the tube rather than cutting into the O.D. the interaction of the ferrules compensates for these variables without the use of inserts for all metallic and semi-rigid nylon types of tube. It is suggested that inserts are used only when installing very soft tubing such as “Tygon”.

Uses long seal area

In the “Leakage” formula developed by the Fluid Controls Institute, it was determined that the longer the contact between the sealing members, the less leakage will occur. This principle has been applied to the HAM-LET design in that the front ferrule makes contact with the full surface area of the body bevel when the fitting has been pulled-up 11/4 turns. No other type of fitting achieves the same level of surface contact and cannot therefore offer the same degree of sealing performance in vacuum or positive pressure systems.

Seals away from the point of heavy work

The HAM-LET fitting seals at a point different from where the heavy work is performed. The heavy work takes place at the interaction between the back and front ferrule during the 11/4 pull-up. The mechanical swaging action and grip is therefore at a point away from where the seal is performed (through 360deg  around the sealing surface of the front ferrule). Geometry rather than torque is used for uniformity of make-up and consistent gaugeability.

Burnishes seal surface

The precision machined front ferrule of the HAM-LET fitting is lifted from 15o to 20o by the interaction of the back ferrule to make contact with the full surface area of the body bevel at it’s maximum available length.  Because the back ferrule acts like a “slip ring”, all the action in the fitting moves down the tubing without twisting in a forward manner. This forward movement of the components brings the sealing surfaces together in such a way that the front ferrule burnishes the body bevel. The result is similar to that of a non-rotating valve stem tip closing on the valve seat.  Burnishing the sealing surfaces provides superior leak-tight connections over a broad pressure and temperature range and allows the connection to be remade many times without replacing component parts. Bite and flare fittings rotate during the “pull-up” and inherently damage or “coin” the body bevel leaving a spiral leak path. Only limited re-makes are possible with these types of connections.

Residual spring condition

Thermal cycling is a major cause of leakage associated with steam systems. This is due to the expansion of component parts during system “Start Up” This is overcome in the HAM-LET tube fitting by the interaction of the front and back ferrule. When the fitting is correctly assembled the sealing surface contact between the front ferrule and body bevel is maintained by the “lifting action” of the back ferrule.

Resists Vibration

High impulse and vibration can quickly cause problems even in the best designed systems. If vibration is not prevented the integrity of the system is likely fail at the point of the fitting connection. In traditional fitting designs the “Olives” bite into the tube and have little or no support ahead of the olives. When vibration is encountered the high stresses can fatigue the tube at the point where the olives contact the tube O.D. and in some cases cut the tube in half. The suppression of this in the HAM-LET tube fitting is achieved by total support of the tube ahead of the ferrules, but more importantly by adopting a design that allows the ferrules to seal on the O.D. of the tubing without creating high stress risers.

Rolled and silver plated threads

It is common knowledge that untreated stainless steel components will “Cold Weld” if no suitable lubricant is applied to the surfaces. This is especially true when male and female threads are screwed together, particularly tapered threads. To prevent “Galling” and to enhance the ease of installation the internal threads on all HAM-LET fitting nuts have been specially plated with a coating of silver.

Used on High Pressure

High pressure can be defined in many ways, 100 PSI is considered extremely high in a vacuum system whereas 6,000 PSI is low in a chemical injection application. The exceptional engineered HAM-LET fitting can be used on both extremes of high vacuum and pressures to the burst point of the tubing and everything in between. It is therefore unnecessary to use many different types of fittings for various applications, the HAM-LET fitting will reduce your stocking levels, eliminate the need to train the installers on numerous types of fittings and more importantly cut costs.


The HAM-LET tube fitting has been used by hundreds of well known Global organisation for the most demanding applications. In-house and outside tests have resulted in the awards of numerous approvals for the product in the Offshore, Petrochemicals, Chemicals, Power, Pharmaceutical, Semi-Conductors and Process Industries.

Globally available

HAM-LET is a global manufacture who has demonstrated a track record of meeting the demands of the supply chain. Establish in 1953 with distribution around the world HAM-LET has the ability to meet and exceed the expectations of the user’s requirements.

Is Self Aligning

It is a common practice for the installers to remove the nut and olive from a compression type fitting then to place them over the tubing prior to re-fitment into the fitting body. This practice is due to the fact that bite and compression fitting olives are not generally machined components and have a tendency to “cock-over” into the bore of the fitting. This makes it very difficult to insert the tubing into the fitting body without damaging the olive and the potential for consequential leakage. The HAM-LET tube fitting is design allows the installer to assemble the fitting without having to remove the components, reducing the potential to loose parts and preventing “dirt” from damaging the sealing surfaces.

Resists Impulse, Pulsation or shock

Impulse or pressure cycling can be attributed to many factors such as quick-opening valves in a hydraulic system. When this situation occurs a considerable amount of stress is applied to the tubing system and auxiliary components.  Conventional types of connections will show signs of weakness because the olives are not supported and have created high loads around the tubing diameter and wall thickness during the installation pull-up. The HAM-LET two ferrule design absorbs any impulse or shock in such systems by eliminating any high stress risers around the tubing and by supporting the tubing ahead of the ferrules.

Used in Vacuum Systems

HAM-LET tube fittings are widely used on industrial vacuum applications. The importance of keeping all action moving in an axial direction with absolutely no torque or rotary motion in making the seal is critical. The axial motion when making joints with HAM-LET tube fittings results in “pressing” or “burnishing” the sealing surfaces together so that there is no scoring or damage to any of the surfaces. Other manufactures fittings (as previously mentioned) damage the sealing surfaces, these fittings are not suitable for vacuum service due to rotation generated during pull-up.

By Graeme Johnston – Director – Valve and Fitting Solutions Ltd