Smaller aparture insert

I believe it was Goosic that mentioned a small rubber insert to fit Lee Enfield ladder rear sites to make the aparture smaller. I'd be curious to know where these can be purchased. Thanks, all!

3 of my #4's have that metal insert installed into the aperture hole. It definitely helps improve aiming.

I have a few of these inserts.  I find a thin sheet (.005 to 0.010 inch) of metal with a peep drilled to 0.05 inch diameter and epoxied to the sight lets more light thru than the insert.  A lot of light is lost thru diffraction in these inserts, they are fairly long, but certainly better than the 0.10 diameter peep on the service sight. 

A national serviceman of the 1950's told me that he and his barrack room mates would block the aperture with soap and pierce it with a pin until they got the desired smaller aperture to classify on the range with. 

We are fortunate here, the CMP Rules allow for a reduced diameter aperture, although does not specify how that can be done. Installing a PH 6c 6 hole eyepiece would clearly be a violation, but affixing a thin sheet of brass (painted flat black of course) to the back of the Mk 1 Singer sight slide would not be considered a violation, nor would be adding a press in insert.  I have found the thin brass sheet works best!