Spacer, $10
This is an empty grating cell. It can be placed between the grating cell and the eyepiece, to increase the spectrum length (dispersion). Multiple spacers can be stacked. These spacers are most useful with telescopes that cannot use the star diagonal technique described below. You may want to wait until you have used the spectroscope a while and have read the Owner's Manual, before buying any spacers. Also, if you have any 1.25-inch color filters, you can remove the glass and use the empty filter cells as spacers.

1.25-inch Threaded Star Diagonal, $49
Page 7 of the spectroscope Owner's Manual describes an optional technique of screwing the grating cell into the star diagonal of a f/10 Schmidt-Cassegrain. This will give a nicely proportioned spectrum when used with an eyepiece of about 26mm focal length. This setup is also useful with slow focal-ratio refractors. But if your brand of star diagonal is not threaded for 1.25-inch filters, you can use this star diagonal. Or if your f/10 Schmidt-Cassegrain is equipped with a 2-inch star diagonal that has a 2-inch to 1.25-inch reducer, you can rotate the 2-inch diagonal 90 degrees and then plug this 1.25-inch diagonal into the reducer.