Abstract: A semi-circular protractor is provided at a center of circle with a through hole to which an auxiliary ruler having a length close to a diameter of the protractor is detachably and rotatably attached. With the auxiliary ruler, the protractor may be used to measure angles on a plane and on a three-dimensional body and to draw different angles. The protractor with the auxiliary ruler is designed for children to more easily understand the meaning of “angle” and to learn to use angles.

Abstract: A union is adapted to butt two reused plastic bottles at their mouths to provide a teaching aid for simulating the forming of spring and convection due to a pressure difference between two spaces. The union includes a hollow tubular body having a radially extended middle partition. An internal screw thread is provided on an inner wall surface of the union at each side of the middle partition to engage with an external screw thread on the mouth of the plastic bottle. The middle partition is provided with two symmetrical through holes, each of which is axially divided into two parts by a radially inward projected annular rib. Each part of the through holes is sized for a suction tube of predetermined dimensions to insert thereinto.

Abstract: A set of universal blocks includes a plurality of uniform-sized cubic elements, a plurality of uniform-sized connecting elements, and at least one disassemble aid. The cubic element each is provided at all six sides with an insertion hole each. The connecting element each is adapted to insert into the insertion holes on the cubic elements and has a length twice or almost twice as long as that of the insertion holes. The disassemble aid is a long flat element provided with a plurality of through holes adapted to easily disassemble the connecting elements from the cubic elements. The cubic elements may be freely connected to one another via the connecting elements to create a variety of two-dimensional and three-dimensional geometric shapes, and be conveniently used to play various kinds of games, including puzzles.

Abstract: Different types of measuring devices detachably built up with different elements are provided. The elements for forming the built-up measuring devices include suitable numbers of connecting rule elements, corner elements, swing elements, fixing bars, and fixing sleeves. The measuring devices that may be built up with the elements include but not limit to ruler, square, three-dimensional square, and arithmetic balance. These measuring devices integrate functions of many commercially available intellectual aids and can be used to take linear, area and cubic measures, practice four fundamental operations, and learn concepts about coordinates.