Some replacement windows come with the flange already installed. Some windows need that built-in flange, plus another one.
Replacment windows will seem to offer less open window space than the original single pane windows. The new windows can be an inch smaller in viewing area all the way around. This is a very important issue. Check the window frame sizes unles you want to be peeking out of a tube instead of a window.
Single hung and double hung windows.
Many of these replacement windows actually snap out of their frames at one edge and allow you to clean them easily.
Some window makers use plastic wheels at the bottoms of their windows and these plastic wheels can go flat because you are not rolling them back and forth two or three times a day to help keep them round. Some window makers use stainless steel wheels.
None of these windows have secure locks. If someone wants to break in they will.
Most all of these windows will come with window screens. Many of these screens will be made of fiberglass and coated with a special plastic. The air moving past the screen causes a static electric charge to be generated which attracts dirt to the screen and so less dirt get inside your home. Other screens are made of aluminum and corrode.
How do they make glass?
Glass is made today in huge factories. Most of these factories receive four full freight cars of raw materials each day. They get special sand, limestone (calcium for durability), soda ash (acts as a flux), dolomite, salt cake, carbon, and iron oxide (to add a slight greenish tinge). Most of these glass factories use a technique invented by Pilkington in England in 1952 called “the float process.”