There are various curls you can use in your lash sets and the one you choose will depend on what look you are hoping to achieve.
There is also a wide range of thicknesses to choose from when lashing but it is really important that when you are choosing you take into consideration the health and thickness of the natural lashes. If the lashes are too long or too heavy it will lead to poor retention and may even cause damage to the natural lashes. Although you can find lashes at a 0.25 and 0.3 thickness, you should never exceed a 0.2. 0.25s and 0.30s are far too heavy for natural lashes to support and will cause the lash to fall out prematurely. A good lash tech will do their best to give the client the look they are after but will not compromise the health of the natural lash. It is important to educate your clients. Your client may want the longest, thickest lashes going but you can only work with what you are given. For example,if they have very thin, sparse lashes there is no way that they will be able to support a 0.20 in a 13mm. Make sure and manage their expectations in the consultation so that they are not disappointed with their new lashes.
Some of the thickness available include
0.03, 0.04, 0.05, 0.06 & 0.07- for volume lashing. These are far too fine to put on individually.
0.10 - You can use these if a client has very fine lashes or double or triple them on each lash depending on the strength of the natural lash. These are great for use when you are capping, stacking and feathering
0.12 - A very popular choice for classic lashing
0.15 - Also popular for classic lashing but best for strong lashes
0.18 - For healthy, stronger lashes
0.20 - Only suitable for very strong lashes. Rarely used