In his latest Deegam Report (number 113), Douglas Myall, author and publisher of the essential Complete Deegam Machin Handbook, has decided to stop distinguishing between Type 1 and Type 2 gaps in the security slits on Machin stamps.
For those readers who are new to Machin Minutiae or who haven't been following this aspect of Machins, I'll give a little history.
In 2009, Royal Mail added several security features to Machins. One of those features was four slits in self-adhesive stamps. These slits were designed to make it hard to remove (and then re-use) stamps that had already been attached to an envelope. There were four U-shaped slits on each stamp, two at lower left and two at lower right, with one slit inverted over the other. The image at the top of this post shows the two slits at the lower left of a 2009 second-class Machin.
Not long after, Royal Mail added tiny gaps to the slits, at the top and bottom of each slit. These gaps were designed to make removal even more difficult. The first such gaps were easy to see with the naked eye, as you can see in the image directly above. Needing a way to describe these varieties, Douglas Myall decided to call the original slits Type 1 and the slits with gaps Type 2.
Soon it became apparent that the gaps varied in size. Some were much smaller than others. A 2009 Machin with small, or narrow, gaps is shown above. In general, stamps printed by Walsall had wide gaps and stamps printed by De La Rue had narrow gaps. Myall decided to call these narrow gaps Type 2a.
By 2011, though, there were gaps of various sizes, and it became difficult to determine where Type 2 ended and Type 2a began. Myall eliminated the Type 2a notation and simply called all slits with gaps Type 2. He then added footnotes to indicate whether the slit had a narrow gap or a wide gap on any particular stamp.
Some of the narrow gaps have always been so small that they are hard to see, even with a low power magnifier. Ian Billings pointed this out on his blog in 2009. I found it useful to use a 30X magnifier, which always revealed even the narrowest gaps.
Recently, the narrow gaps have gotten even smaller. Myall points out the £1.52 value issued on March 24 of this year and says that some collectors have considered this stamp to be Type 1 because the gap is so small.
You can see from my scan above (all scans shown here were done at 1600 dpi and not altered in any way) that the gap in the 2015 £1.52 is slightly smaller than the gap in the 2009 second-class Walsall stamp, but the difference is really microscopic.
So now in the Deegam Handbook, there will be no security slit types in the description of stamps. Myall notes that there are a few instances where otherwise identical stamps have more than one type of slit (I believe these are mostly from early business sheets), and these will be described with a footnote.
Personally, I still consider the distinction between gap and no gap to be important. I discontinued the Type 2a notation when Myall did, but I am going to continue using Type 1 and Type 2. If I can see the gaps with the 30X magnifier, then I will consider the stamp to be Type 2. After all, there are other characteristics of Machins that require a 30X scope to be seen clearly, such as phosphor screen, so the presence of a gap in the security slit is just another one of these.
(Myall and others recommend the use of a 10X magnifier for identifying Machins, but I have found that a 30X, with a built-in light, makes identification somewhat easier.)