Heidi Swapp Lightbox Alphabet Inserts - International Black. Create clever signs with international Lightbox alphas. Simply arrange letters for a fun look to parties, weddings and home decor. The possibilities are endless! This 3 1/2 x 3 3/8 x 1 1/4 inch package contains fifty lightbox inserts. WARNING: This product contains chemicals known to the State of California to cause cancer, birth defects or other reproductive harm. Do not mouth or chew. Imported.