I am often horrified when I see clasp knives listed for sale and the accompanying photo’s show the knife with the blade, marline spike and tin opener all deployed. I guess this is a simple mistake for people not familiar with the damage this can cause.

The advice that I am going to give here can equally apply to all multi bladed clasp knives, even those of modern manufacture. You may have already been told why it is not a good idea to deploy more than one blade at a time. I hope to simply explain why.

Let’s look at the construction of the typical Military clasp knife. The knife has a blade at one end, a tin opener at the same end and a marline spike at the other end. There is also a screwdriver stub as part of central liner. On either side of the central liner is a back spring. This spring applies the pressure that keeps the blade, spike or tin opener in place when either closed or open. The outer liners are also the scales. It is a simple slip joint construction with no locking device.

The problem is that these back springs can break. There is light pressure on the springs when the blade, spike and tin opener are in the closed position which stops the blade, spike and tin opener moving until deployment. The spring applies firm pressure when the blade, spike or tin opener is open to hold them in the working position. The maximum amount of pressure is applied when the blade, spike or tin opener is in the half open position. The most severe pressure that can be applied to the back spring is if the blade or tin opener is half opened and the marline spike is then opened at the other end, when the marline spike reaches half way it applies the maximum pressure to the other end of the spring.  This can cause the spring to break.

The back springs on WW2 knives can be very brittle and are subject to breaking. As a result, these knives sometimes turn up for sale with broken back springs. It is a good idea when you see a clasp knife offered for sale to ask if the springs are in good order, does the blade, spike and tin opener open and close with snap. This is referred to as “Walk and Talk” It is also worthwhile asking if the blades have any sideways movement or wobble when open. The more modern Stainless Steel clasp knives are also subject to back spring failure.

Sometimes these springs just break.  Sadly, I have had springs break when just opening a knife carefully to take a photograph of it. I know of other collectors who have had this happen also. Believe me, it is heartbreaking, as in my case it was with one of the harder to obtain Whittingslowe Product No: 47 clasp knife pattern and that pattern doesn’t even have a marline spike.

In a perfect world where the springs would be perfectly tempered, one would not need to have to worry about the springs. However these knives are made by people and people are not perfect and sometimes the steel simply has flaws in it. I am sure that the expedience of war time production meant that the clasp knives were produced as quickly as possible to get them to the troops. I doubt that anyone at the time envisioned that these knives would still be in service 70 years later or even the subject of collectors discussions. My preferred display position with the 3 blade clasp knife is with the blade at right angle to the scales, the tin opener at 45 degrees to the scales, with the spike closed. If I wish to show the spike deployed I will close the blade and tin opener.  

The same advice is valid for modern slip joint knives with multiple blades. I expect that the failure rate is a lot lower on modern quality knives but failures do occur. No matter how careful the maker is, the steel may still have flaws. If it happens when you purchase a new knife you can normally replace it under warranty. Not as easy many years down the track when the knife is much older. As for our WW2 artifacts; what we have, we have to look after.

So what does this mean to the collector?

Does it mean that any knife with a broken spring is worthless? Not quite. It does considerably devalue a knife if it has a broken back spring. For a start it is useless as a user and is only suitable for a collection. Some of these knives still serve as users. After all, the WW2 knives were made from good quality materials at the time. They are generally a robust well made knife and the carbon steel blades hold a good edge. If the spring does not fail it will give many years of service. Even with a broken back spring, if the knife is a hard to find example it may well be worthwhile adding it to your collection until a better example comes along. Even then, if it is a common knife such as any of the Whittingslowe clasp knives, a knife with a broken back spring can still be part of a display. Normally with a broken back spring the blade or tin opener will just flop. I have taken such knives and fixed the blade in place with strong epoxy adhesive. If the knife is in the display position and is not going to be handled then this is not a problem. However, if and when the knife is sold or even given away it is incumbent upon you to inform the new custodian that the knife is flawed.

I have made a couple of displays by turning an old picture frame in to a shadow box and mounting the knives in that. Once the knives are behind glass they will not be handled.

This information was featured in the Australian Knife Magazine, Issue 3 Feb - Apr 2018 in the Military Collector column.