Raleigh provided a variety of handlebars and stems for the Raleigh Twenty over it's 18-year production run. They work well, but may not always suit your needs. Several members have already converted to drop bars or butterfly bars. This page aims to give you an over of your options when upgrading the stem and handlebars.
The Nitto Technomic is the tallest alloy stem on the market today. It is made of forged aluminium in a range of forward extension lengths from 50mm to 120mm. The overall height is about 225mm (about 9 inches) which is a few inches taller than most other stems on the market.
The stem end is 25.4", so accepts a 1 1/8" Ahead stem with a 1" reducing shim. A hacksaw and file are the only tools necessary for making a simple stem riser for a Twenty. An aheadset is also shown on the bottom-right of the photo.
The fat, straight 1" diameter mid section of the donor bar (now the upper end of the conversion shaft) is where the Ahead stem clamps on. The bar's mild 'backsweep' bend provides a useful forward extension when used vertically as a stem riser. This is a simple and cheap way to get a strong, light and effective stem riser that will take any Ahead stem.
Soma Fabrications also made a nice aheadset stem quill converter.