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About Thumb Indexes

Indexing machines, ca. 1905. (Courtesy US GPO)

The following query appeared on this site recently:

Please, I would like to know the term used for the “thumb indents” found in older hardbound dictionaries, one at the start of each new letter. Also, was making these indents considered part of the binding process, and how was it accomplished? 

The proper term is “thumb indexes” and there were, and are, machines that cut the indentations. A tab or label with the appropriate letter or title is then affixed. It is a bindery operation.

The U.S. Government Publishing Office (formerly the Government Printing Office), operated a mind-boggling array of equipment in the early twentieth-century. By 1942, GPO’s catalog of machinery listed eight indexing machines by three manufacturers. In the 1980 catalog, seven machines were listed, although some of those are for cutting strip indexes rather than thumb indexes. The photo above  shows workers in the Bindery operating indexing machines, about 1905.

GPO’s apprentice school published its own textbooks throughout most of the twentieth-century. The chapter “Miscellaneous: Rounding Corners, Indexing, Numbering ” in the textbook Theory and Practice of Bookbinding (1950) gives the following summary of fore edge indexing:

Three kinds of index are in general use. One is the cut-in or strip index, in which a strip is removed from the margin of the page leaving a portion of the margin upon which the index number or letter is printed. Another is the thumb index which is a semicircular indention cut in the page margins. Another is the tab index which consists of numbered or lettered tabs pasted to the page margins. Indexes for reference books usually are of the thumb or the tab variety, while account books generally have cut-in indexes or occasionally tab indexes.

To machine cut a cut-in index, the guide on the machine is set for the depth of the cut and the ratchet is set to space the divisions. The book is fastened in the clamp and the operator lets the pages fall on the cutting blade. As each division is cut, the machine shifts the book along for the next cut.

The cut-in index can be cut by hand also. The divisions are marked off on the pages and index shears are used to cut in at each division mark. Index shears are equipped with an adjustable gage to cut to the desired depth. A cutting zinc is inserted between the first and the second divisions. A straightedge and knife are used to cut parallel to the fore edge through the first division from the shear cut to the tail of the page. The other divisions are cut in the same manner. The letters are then marked on the divisions by hand with ink.An indexing roll with the alphabet on its edge should be used if much work of one size is to be indexed. The spacing between letters corresponds to the spacing between divisions of the index so that the entire index can be imprinted by running the roll along the index divisions. The cut-in index can be reinforced by means of a piece of heavy paper, cloth, or leather folded around that portion of the margin that carries the index letter. This should be done before the index Is cut so that the blade will cut the reinforcing material with the page.

The thumb index is cut with a semicircular cutter. One kind of cutter resembles a pair of pliers and is operated by hand, and another is operated by compressed air. The Index divisions are marked and the cutting plate is slipped between the pages on top of the first division page. The book is forced back so that the fore edge is at an angle and the thumb notch is cut. The division letters or numbers are stamped on semicircular pieces of reinforcing material such as cloth or leather, slightly larger than the thumb notch. They are pasted on the division pages directly under the notch, which may be colored by the use of edge colors applied with a small brush. If the book edges are to be marbled, the marbling should be applied before the index is cut.

Thumb indexes can be cut by hand by the use of a half-round chisel of the proper size. A piece of binder’s board for the chisel to cut against should be placed in the book at the division page. This is a slow process and is suitable only for occasional use.

Some of GPO’s fine work for Congress still requires thumb indexes. A hand-held device has replaced the large models in the photo. We produced a video about the binding of Jefferson’s Manual a few years ago, which walks through the process of binding an edition of the manual in leather, including the cutting of the thumb indexes. The link is to a short clip of that process.


  1. I found this fascinating. As the Historian of Bills for many years I have seen a lot of changes. We indexed on carbon index cards and sent those to GPO typesetters. Thumb Index methods, like our use of computers today, is definitely different. I enjoy looking at the old pictures of GPO workers and the equipment they used.

  2. I am curious when the first thumb cut index tabs appeared.

  3. Steven Edward Grissom 24 September, 2019 at 11:29 am

    I have been looking for a type of bible thumb indexing that indexed all the way down to chapter if not verse. I had a bible cut this way at one time and was told there were only a couple of machines left that do it and only one worked. That bible became my sons bible as a hand me down 15 yrs ago. Now it has black mold on it and we will have to get another but he wants it exactly the same as it has emotional value to him. Please help, I don’t even know where to begin this search for someone that can do it or has the machine but I thought you may have a better idea than me.

  4. Mr. Grissom: I don’t think I have any direct suggestion, although someone else may respond here. You might consider posting a query to Briar Press (, an active discussion forum made up of many working printers, some of whom might have an idea. Alternatively, a bookbinder with experience in restoration might also have suggestions about the mold problem. The organization for hand bookbinders is called the Guild of Bookworkers ( Best of luck.

  5. I have a Rhema study bible.. that is thumb indexed but some of the tabs have been lost.. the only problem I have in finding replacement half moon tabs.. is that.. it appears this bible was NOT indexed in the usual way.. in that the NT tabs follow the usual way of indexing.. but the old Testament tabs.. are not facing the same direction..the O.T tabs are facing as if face to face to the N.T. tabs.. it appears when this bible was indexed that the indexers turned the bible over with its front side facing down to do all the tabs for the Old testament.. so the tabs for the O.T. begin with the lettering on the arch side Not the flat side of the half moon..the O.T. tabs are used with the left thumb and the N.T. tabs are used with the right thumb…any answers as to how I can find O.T. replacement tabs for this with the wording facing properly.. in accordance to the tab location?…

  6. Where can I get large aphabetic thumb index replacements for my Strong’s Bible Concordance?

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