Appropriate filament selection depends on your research application.

Box Filaments are recommended for small to large diameter borosilicate glass, double barreled, or aluminosilicate glass. Box filaments are particularly suitable for patch pipettes, slice preparations, and for sharp electrodes and microinjection pipettes where gradual parallel walls would aid cell penetration. When using a box filament, the size of the square box should be approximately 1.0 to 1.5 mm larger than the outside diameter of the glass that you will be using.

Trough Filaments are excellent general purpose filaments and are recommended for creating longer slice patch pipettes and sharp electrodes. The trough filament is not ideal for making patch pipettes or when using glass over 1.2 mm OD. If very short tapers are required for patch electrodes or for microinjection, a 2.5 or 3 mm box filament is recommended.